Let’s Find The LCD (Lowest Common Denominator) … Step-by-Step…
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- เผยแพร่เมื่อ 17 ก.ย. 2024
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Math help with how to find the LCD (lowest common denominator). For more math help to include math lessons, practice problems and math tutorials check out my full math help program at tcmathacademy....
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I knew what I was doing until you began explaining. Thanks for teaching me to forget how to do math.
Next time just build a separate fraction from the denominators, then reduce that fraction, and find a cross product between it and it’s reduced form. Behold:
20/32 reduces to 5/8. 20x8=160, and 32x5=160. The LCM is 160. Works every time.
The method in the video is very convoluted. Your way seem much simpler.
Try your method with 19/32. He perhaps should have chosen a fraction which did not simplify but he was demonstrating finding LCMs by using factors, nor fractions.
This helped me throughout my journey, thank you.
@@brianreay4104 19 is a prime number, so no factoring is available.
VirtualBilly the method that you used is the one that I was taught in Canadian grade 8 by a great teacher in both Arithmetic and English Grammar. Mr. Carter taught that BOTH subjects had rules.
I’m happy that you remember a simple way to compute with fractions. As a math teacher for elementary and middle school kids some of whom had a variety of learning difficulties, I can tell you that his approach is excellent! It is easy for people to learn time-saving tricks for solving homework and test problems, but if that is all they know, they won’t have the foundation to truly understand mathematics, especially for higher level math. Math won’t be available as a problem-solving tool in everyday life. How many adults say of math, “I used to know how to do this”. If those folks had learned all the steps of the particular process, they’d be able to work a problem out. Teachers know what they’re doing.
Why not just multiply the denominators together, so 20x32=640. Then do 5x20 + 3x32 =196 for the numerator. Then just cancel the fraction 196/640 (often just halve both numbers repeatedly) until it's in its simplest form, ie 49/160.
That's exactly how I did it. Old school is best!
This is how I was taught!
Yes, same for me too. Less thought involved all round and easier for students to follow.
Yes, but you have to deal with bigger numbers without LCD.
@@DarVV But what is easier to students? Multiplying two numbers together to find a common denominators then cross multiply or know and be able to use factor trees as done here?
This presentation is a good example of why people hate math. You take a simple question and spin off into never never land and at the end it’s WTF how did we get here; like you’re making it up as you go along.
They old way is much easier.
I think this is common core..why ihate common core...
@@shirleyyenktesh4270 yea
Is the answer 49/160?
I never had a problem finding the LCD since grade school, but watching this video
I'm thrown for a loop. This is just is worst then common core math. KEEP IT SIMPLE
Another way is multiply the two denominators together convert the fractions and then reduce to lowest terms
There you go. Fastest way.
Multiplying denominators does not assure LCD!
@@rogermosberger6856 You will end up with the LCD when you reduce the solution to lowest terms.
20 = 4*5 ; 32=4*8 ; You can always multiply by one so multiply first term by 8/8 and second by 5/5 = 24/160 +25/160; thus 49/160
This is how I was taught. Much easier.
I don’t worry about finding the LCD so much. I use the bow-tie method to solve fractions. Multiply 3 & 32, 20 & 5. Add those 2 totals together to get Numerator. (196). Multiply 20 & 32 to get Denominator (640). Then reduce to lowest terms. 196/640 = 49/160.
Well of course you don’t worry about the LCD when solving fractions. Nobody does. This is because the GCF is used to solve fractions, not the LCD. This video isn’t about solving fractions though, it’s about finding the LCD, which is a valid, completely unrelated process altogether.
And to clarify, generally when we say “solve” a fraction, we’re talking about reducing it, not performing an operation on two or more of them. You’ve combined the two fractions in this example, but again, the focus is on finding the LCD.
Old School math is easier. 1957 - 1976.
? as in ?.
I agree sir.
Common core dumbs down kids i hear although they claim opposite..to me it makes your mind slower.
You get to a point and enter powers into the conversation.
Then dismiss it.
Take it from a guy that can take math from here to approaching infinity and still get a D (see what I did there?), that some learners would lose focus.
The relationship between LCD & LCF might be emphasized.
Multiplying the denominators and cross multiply the numerators before reducing is cumbersome, but always works.
By the time he gets to the end i have forgotten what he was doing in the fist place ?.
Yes, the more cumbersome methods work, but the whole reason we have mathematics is to simplify our problems before we solve them, so that 1.)they’re easier to solve, and 2.)we’re therefore more likely to come to the correct solution. There’s no shame in doing math the easy way.
🤔 🤪 I'm so glad I went thru old school! 😂
Thanks for posting this video. Never before, in a little over 11 minutes, have I so easily been able to understand what is wrong with the American educational system. Now I know why the proficient math personages are coming to our country from Asia and why so many of our students say they hate math.
Just for fun, I started working on the problem on my own when you began talking and I had my solution before you had introduced yourself. And when I looked at my paper it had 5 numbers on it which included the solution.
As many of these TH-cam videos state...we are doomed. PS - Yeah, I'm a 68-year-old SOB who learned how to do math for use in the real world.
I'm only 61 and worked this out quite quickly : 20 = 4x5, 32 = 4x8, so eliminate one of the 4s and 4x5x8= 160.
@@MaxTSanches Same here.
Wow are you special Max.
Oh for goodness sake I’m glad I got taught decimals in the UK , this is an absolute headache , neither wonder kids are confused 😐
Fractions are easy, this method is a nightmare. I did this in my head in 15 seconds or so.
I converted them into decimals, too. From USA…
To determine the LCD, in my head I looked at the 20 and the 32. And I thought that the LCD would have to be a number ending in 0 otherwise the 20 couldn't divide into it. So I quickly multiplied 32 * 1, then * 2, then * 3, then * 4. And none of those answers end in a zero. And when I multiply 32 * 5 I realized it was a number ending in 0 or 160. And l knew both numbers could divide into it. Poor explanation but it worked for me.
Goodness gracious! Thank goodness you never taught me maths! Had it figured in less than a minute. Good old fashioned way. Way too complicated.
You made it too complicated. Just use 20x32 as common denominator. Add 3x32 + 5x20 and divide by 20x32.
Simple, not complicated, easy - when you have a calculator (which everyone does), and it works. The LCM was for when I learnt arithmatic 55 years ago when no one had a calculator.
Ikr
Just list the lcms
20: 20, 40, 60, 80, 100, 120, 140, 160
32: 32, 64, 96, 128, 160
Now we have 160
20 used 8 times to get there
33 used 5 times to get there
3×8 over 20x8
5×5 over 32x5
24 over 160
25 over 160
24+25 = 49 over 160
Cannot be broken down more
Final answer is 49 over 160
You have an incredible talent for making easy things difficult,through roads back and forth. In the end we got lost.
@efiskordili4606
Speak for yourself.
This reminds me of Covid when authorities said that they would flatten the curve ... still going on to the letter 'O' (omicron). Eleven minutes and fifteen seconds (11:15): Well, that's why I had dropped out of math class in my teens. One example took up the entire blackboard which was 10 times larger than by little book, so I gave up. Now I can master the LCD by simply cross multiply the denominators.
OMG.. this guy makes it so hard. Just multiply 32 over and over until you get a number 20 with divide into. 160. 32 went in 5 times. 20 went in 8 times. Use 5 and 8 to multiply the top numbers. Add both and get 49/160. This took me less than 5 seconds.
I agree. This guy always makes simple problems complicated. But easier than your idea, with 20 as one, we know the other will have to end with a zero. 5 times 2 will give us that. Pretty close to the same as yours. No offense if it comes across that way.
훌륭한 계산법 입니다
Oh dear maybe I should take up knitting
He is teaching a specific method - the prime factorization method.
20x32=640
then (3x32) + (20x5) =196
So 196/640 as both are divisible by 4
answer is 49/160
LCD I learned that in the 60’s, did it in my head in less than 30’s John takes time to detail the process once you have it in place it’s easier than blindly multiplying the denominators and you skip the simplifying process at the end!
Congratulations. You've just made simple mathematics, difficult.
Exactly. This guy is ridiculous.
This is a great example of taking a challenging problem and making it extremely difficult. This guy is pitching his line of math classes but not showing how to solve them. He obviously is in love with the sound of his own voice.
Teach it this way if you want to instill a dread of mathematics in a 7th grader. Leave out the factoring nonsense.
This guy doesn’t get bored of math!!!
Couldn't agree with you more. This guy is full of shit and couldn't teach in a simple way to save his life.
😂🤣😂🤣
Man! I was blessed being taught by the teacher I had. I quit this video a quarter of the way. He put me to sleep even after a go 8 hours night sleep.
I teach primary school Maths in Singapore... Been doing so for quite a few years. At some point I started asking what the lesson was about: addition of fractions or finding the lowest common denominator (multiple).
Actually, you don't need the least common denominator, just _a_ common denominator. Convert the two fractions and add. Easy to reduce if not the lcd. Often much simpler.
20 = 4*5 ; 32=4*8 ; You do not need to bother with the common factor 4. You can always multiply by one so multiply the first term by 8/8 and second by 5/5 = 24/160 +25/160; thus 49/160
I’ve always thought The Denominators would be a great name for a metal band.
Just use 1950’s and 60’s math to do this in half the time. New math is B.S.
It sure is! It took me 5 seconds to figure. Could be I'm a product of 1950's- 1960's when many people thought outside the box and logic & common sense was common. We were taught how to think not what to think!
Agree
@@stanzilinski8123 Common sense .... isn't that classified as a super power now?
ahem…what is 50’s and 60’s math? I flunked that too. Lol
lol This isn’t “new math,” it’s prime factoring, and we’ve known about it for centuries.
Since I learned to perform this operation 65 years ago and I cannot find my 5th grade math book, the only way for me to solve it now is to convert both fractions to decimals, add the two decimals, and then look up the sum on a decimal equivalent table.
Retired since 2003, I have little need to solve fractions. The fact that I spent; 24 years in classrooms, 31 years working in factories, on Navy ships, and as an RN in emergency trauma hospitals, I am troubled by the fact that I can no longer solve it the way Mrs. Albee taught us at age 10,
What???? You belong in "Ripley's Believe it or not." You must be the only living person who solves fractions by converting them to decimals.That's okay if you're talking about fractions like 1/2, 1/4, 1/5, 1/10, but what about MOST fractions? I guess you are happy if your answer is approximately correct. How close does it ave to be?
@@quabledistocficklepo3597 ,
In my world, mathematics which has NO practical application (AKA "pure") is little more than mental masturbation.
As is readily aparrent to the most casual observer, your mathematical acumen vastly supercedes your reading comprehension.
I believe I explained how I might have arrived at a plausible approximation were my life to have depended on it (such as calculating my re-entry trajectory from space) but being retired for nearly 20 years, I cannot generate sufficient interest to POSSIBLY give a fat rat's ass.
49/160 in my head in 20 seconds.
675 seconds in plus reading time of these comments to get the answer. Thanks Terry :-)
What took you so long?
That’s 11 minutes of my life I’ll never get back !!
This video shows how to turn a very simple thing into a very complicated one. Just do 20 * 32 / 4 = 160. (Divided by 4 because (32*20)/20*3 and (32*20)/32*5 are both multiples of 4)
I did it in my head before i played the post🤓; I am so thankful I paid attention in school.😌 That was fun. Thank you.👊🏾☺️
@Ceijonius
I did it in my head, too. I got 49/160, and I see others got the same answer. I'm not going to bother checking.
thanks man I was having so much trouble with this. I'm homeschooled and my mom is also not the best at math so this really helps.
LOL ! I just read through the comments and TEACH , you just got stood in the corner ! LOL. 49/160 . . . , any ole grandparent knows that ! 8 )
In my head, 3o seconds, finding the LCD is the key, Scottish education primary school level in the early 1960s.
Multiply 20 by 32 gives you a common denominator. 640
It is not lowest, but it works.
Then is 3 x 32/640 + 5 x 20/640 = 196/640.
Then look for the LCD.
Much simpler and quicker.
LCM=160 3/20=24/160. 5/32=25/160. 24+25=49 49/160 Ans
Glad I had a maths master who made it exciting, not how cleaver I am
That’s to much work for when you have to solve that problem under a timed test.
Not if you practice and have a facility for factoring. I saw instantly that 20 = 2x2x5 and 32 = 2x2x2x2x2. It can get difficult if the denominators are very large like 657 and 486, but those problems are found on harder tests on which you are given more time.
Too complicated. Teachers like you are the reason why I hated math a a teen
The example used has been made far too complicated. It’s much easier then demonstrated.
49/160. I got it. Thanks, Bowtie works! Just keep on dividing by 2 until you cant go any lower.
196/640= 98/320=49/160
Why didn't you divide by "4", instead. LOL
I was just teaching my daughter how to find the LCD for smaller numbers last night. This video will come in handy when the numbers get larger. I have used factor trees to find larger square roots but haven’t used them to find the the LCD. Thank you!
11 minutes to tell me something I knew in five seconds simply by looking at the fractions
Hey very good my method took less than half the time and got the right answer
Everybody always looking for the common denominator. I figured it out. It took a while and I had a good teacher.
(3/20)+(5/32)
(24/160)+(25/160)
49/160 ✓
I can do it fast and easy. Since 20 is one of the numbers and ends in '0' thwn the LCD has to end in a '0'. Start with 2. 2 x 32 = 64, then 3 and so on till u get to 5.Therefore 5 x 32 = 160 is the LCD
Yeah u right to a point because the other demonater also has to divide in evenly also :)
@@OU812NVME That's why I explained it the way I did. THE WHOLE PURPOSE OF MY EXPLANATION WAS TO SHOW A MEATHOD TO FIND THE LOWEST LCD.
That's exactly what I did; however, numbers ending in "0" are divisible by 5 and/or 10. Thus, you don't have to start with 2, 3, etc; simply multiply the non-zero number by 5 and go to 10, if necessary.
Thanks for every math video you post..
Bring a picnic basket. The slowest teacher since Gandhi.
You got to be out of your mind to subscribe to this guy
All those old people who go on and on about the good old days? Well there’s a reason why they’re called that.
(8 . 3 + 5 . 5) / (5 . 32) = (24 + 25)/160
= 49/160
the way you explain how to solve this makes it more harder...
I was always taught to multiply the denominators and divide by 2. Then by 2 again. Or multiply denominators then reduce the fractions. Either way got me to 160 a lot easier than this.
if one of the numbers isn't even then you can't rely on dividing by 2 repeatedly. The long seemingly time-consuming method is so you learn a solid foundation that can be applied to harder problems as you progress. All these critics in the comment section seem to miss the point entirely. They just want shortcuts and "hacks" and then wonder why they can't pass more advanced math classes.
I learned this method decades ago, AND I STILL REMEMBERED IT. Don't tell me I'm over the hill.
What a complicated method for a simple task.
49/160
I assume you immediately did what I did: 20x32=640 as an initial common denominator.
Sheesh, the guy turns the problem into rocket science!
@@richardsilva-spokane3436 it's a good last resort. Or fifty years ago it was.
Now we all carry a calculator. Understanding the mechanics, or rather the steps to expand before, and then reduce the fraction after the addition are the salient points.
Have to get to 0 lowest is 160 so 49/160 done
Is this a Common Core Math
model/ procedure?
I go to the comments to actually understand how to get the LCM. Is there someone other than this guy that knows how to teach math, so I don’t have to waste my time and go to the comments to get the answer.
Just 32x20 for denominator. Then just work it out. Then slowly lower term if possible. Lower term slowly ➗ 2 and 3 slowly isn't difficult for kids 🧒
You're making the problem complicated...make it simpler!
Agree, it seems he doesn't want his student to learn math easier way. LOL
The sole purpose of these video’s is to make the people commenting feel like they are better and smarter than the instructor. That’s the only reason he makes them.
Thank you
Strange. I suddenly have a hankering for school lunch....
You lost me completely. It was easy to figure how to do the sum before you complicated everything and if this is how maths is taught in school it's probably one reason why I get blank stares from cashiers working out change of a £5 note for a 99p purchase.
Never really cared for math but this fun!
Long way
What's the answer you made it a lot more than what it should be
I don’t use all of that and I got the lcd in less than a minute. You are making it way to complicated. Sheesh!
Bro I was promised some LSD where the tabs at
ROTFLMBO
This is stupid. Why do you need the lowest common denominator? This is useless complication; we're adding difficulty that contributes nothing. Simply, ANY common denominator will work just as well. Putting unnecessary complication to elementary computation merely discourages our young students from pursuing serious math.
If any one thinks this is complicated ?.
Wait till you get to the video on simplifying !. your head will be spinning like you are possessed ?.
By the time you get to the answer , You have forgotten what the question was ?.
I keep it simple. 20 is divisible by 4. So is 32. 5 is prime. I know I am done. Multiply 32 by 5 since that's what is left for the first denominator. That's 160. Can't do math in your head? Think about it in terms of money. That's 32 nickels or $1.60. Some people are good with money and can relate it that way in their head. Anyway, I doubt this video covers the numerator. We multiply 3 by 8 since 32 divided by 4 is 8. We multiple 5 by 5 due to what I previously discussed. We add those numbers together, 24 and 25, giving us 49 for the numerator. The factors of 49 are 1, 7, and 49. 160 is not divisible by 7 so the answer to this problem is 49/160, if instructed to actually solve it. What percentage is that? Well, 160/1.6=100. So 49/1.6 is the answer. Can we do that in our heads? 48/1.6=30. That leaves 1/1.6, which is the same as 5/8. That is also the same as 60/96. Look against at 5/8, which is the same as 2.5/4. 60+2.5 = 62.5, which means that 5/8 is 62.5% of 100. Now we know that 49/1.6 = 30.625 since 62.5% = 0.625, and we just add that to 30. However, it is good practice to answer a fraction problem by leaving it in fraction form. This is just for anyone who is curious about what it converts to and how to convert it in his or her head. Note: anything in percent form is converted to decimal form by dividing the number by 100
This guy must be paid by the hour that is why he makes a simple problem into a complicated.
So what's the final answer???? x/160??
24/160 + 25/160 = 49/160
I used the LCD with the buttons on it. (Liquid Crystal Display)
Do you know what to do if none of your numbers are not the same
Why did?n't you complete it?
5
-
160
+
3
-
160 =
8
-
160
Reduced to I
-
20
Every comment negative, yet a 4:1 up to down ratio - now that's some interesting math.
LCD on those fractions should be (4) not 160 ?
4 would be the GCF of the denominators, not the LCD of the fractions. You probably need these videos.
I'm glad you were not my math teacher..
or look at it and easily determine 5 x 32 = 160 answer is 49/160
Turn them upside down to divide in even numbers.
Thx
There has got to be an easier way?
There is don't do them .
Wtf complicated. So basically you need 32 to get to a 0 as the ones digit which means either a multiple of 5 or 10. 5*32=160 20 goes into that 8 times. 3*8 is 24 so 24/160 and 5*5=25 so 24/160+25/160=49/160.
This problem doesn't need a "Factor tree" cuz five two's = 32. LOL
I hate math after watching this .lol
Love your class! But I would point out that 20 divided by 160 is not 8. Just saying ;)
5:30 You said MKAY four times in 15 seconds. Does anyone in your family, by any chance, teach at Southpark Elementary?
No wonder students give up maths
Ok 20 = 4×5 and 32 = 4×8. So lcm is 4×5× 8=160. Is that ok with you
U made it very complicated
This is why it takes 12 years to get through school
Lcd 20= 20/2;5;2 lcd 32=/2;2:2;2 ;2and the common factor=160then it is easy
What is the answer ?
What is new technique?
Wow. i figured out that 160 was the LCD just by looking at it for a few seconds. Is all this really necessary?
make it short explanation
Très compliqué!je préfère ma méthode.Réponse est49 sur 160