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The way I solved it is by knowing that he will drive for 7 hours. He is going 40 and returning at 30 so you can estimate that he will be going 40 for around the first 3 hour then returning at 30 for the last 4 hour. You multiply 40 with 3 and 4 with 30 , you will get 120
That's a specific sense not everyone has it, your solution could solve the problem in less than 10 seconds, but not everyone familiar with this kind of troubleshooting ;)
the way i solved it was: 40 * 7 hours = 280 /2 (round trip) = 140 30 * 7 = 210 /2 = 105 therefore the trip has to be less than 140 but more than 105. and i got the answer of 120
I found the same result in 15 seconds just plugging in solutions, and usually the mid-solution is the one to start from; GMAT is not about finding the most correct way to solve a problem, it's about finding the smartest way
Yep, great approach! And that's what I teach in my non-standard GMAT math strategy lessons: www.dominatethegmat.com/video-purchase/a-la-carte-topics/gmat-strategies-non-traditional-math-techniques/
This is Physics, when I was in junior high school the formula is v = s.t, s=v/t, and t=v/s V stands for Velocity S stands for Speed T stands for Time he is correct in resolving the problem by looking for the t value, then apply that t value into the formula. Maybe if you can speed up the process, that'd be great. Resolve one GMAT problem is like chasing the time :)
One of your strategies is to work backwards on problem solving questions if the answers are all numbers. Could you do that for this type of question? If so, could you explain how?
+Anthony DiDonato Yes, absolutely. And in fact that's probably the more efficient way to solve this problem! Start by assuming the correct answer is C. IF he drives out 145km into the desert at 40km/h, then it will take him 145/40 = 3.625 hours. Then on the way back it'll take him 145/30 = 4.833 hours. 3.625 hours + 4.833 hours + the 1 hour for lunch = 9.458 total hours, which is MORE than the 8 hours the problem says he spent. So answer choice C is wrong. It's also too many hours, which means 145km is too FAR, so answer choices D and E are also out. Now try A or B. If we try B, it'll take him 120/40 = 3 hours to drive out, then 120/30 = 4 hours to drive back, plus the 1 hour for lunch = 8 total hours. That works! Answer choice B.
It's because the amount of time that he'll travel on the way back is different from the amount of time he'll travel going out, so we can't just let "t" be the time both directions. The problem gives us clues as to how to account for the difference in time. Specifically, we know he'll be traveling for 7 hours total (the 8 hour travel time minus the hour he stops for lunch). So we represent that as 7-t. For example, if his total travel time is 7 hours and it takes him 3 hours to go out, how long will it take him to return? Four hours, obviously. It's easy with real numbers. But since we don't know exactly how long it takes him to go out, be use the variable "t" to represent that.
I dont know if this method is applicable for all questions so let me know if this is limited in solving other qs. But since distance is the same and since velocity is d/t, I just looked for the least divisible number of 30,40 which is 120, so I didnt calculate any time.
That's good reasoning for a question like this. Insightful! For anyone else reading this comment: Velocity is NOT tested on the GMAT, so focus on learning GMAT-specific math and reasoning strategies.
No, because that would mean that he's traveling one less hour on the way back than on the way out, but that's not what the problem is saying. Their times are respective to the total eight hours (minus the hour for lunch on the way back in the case of the return trip), not relative to each other.
Thanks for your videos. I have an observation: the distance drove was two times the same distance, not only one way, so the correct answer should be 240, right?
That would be the total distance for the entire round-trip. However, the question only asks for how far Steve can drive "into the desert," meaning only the "out" portion of the trip.
"t" represents the amount of time it takes Steve to drive out into the desert. The amount of time for his return trip will be different since his rate is different, but we still want to represent it in terms of "t" so that we only have one variable. The best way to do that is to simply subtract "t" -- the amount of time he's already traveled going out -- from the total trip time; the difference is his return time. So what is the total trip time? Well he spends 8 hours total away from home, but an hour of that is sitting still for lunch. So the actual travel time is 8 - 1 = 7 hours. That's why the return time is (7-t).
@@dominatethegmat Well, "spending eight hours away from home including a one hour lunch break". Is it only during returning? Also, I thought that one hour of lunch break was included in that eight hours. So, if that's included, why was it substracted?
@@shafiabdullahhauque7933 The time you're solving for is travel time, so you don't need to account for the one hour for lunch. It doesn't matter when the lunch break happens (i.e. whether the lunch break happens on the way out, before returning, or on the return trip is irrelevant), it simply needs to be subtracted from the 8 hours.
I tried to solve this question by using a different method and I couldn't get a right answer. R=40kph+30kph=70; T=7; D=2y . Given that R*T=D, I found y=245. I am not sure why my formula is incorrect.
You can't aggregate everything that way. Since it's a round-trip situation where the rate and time is different going and coming, you have to treat each individually. At no point is Steve going 70mph, so you can't use that as his collective rate over the entire trip.
It wants to know how far he can "drive into the desert". So you wouldn't count the distance traveled on the trip back. You can take his average speed which would give you 35km/h. All you need to do is take half of the total distance. D = (35 km/h)(7h) = 245 245/2 = 122.5 The answer is B
RAHUL Sahni Hahaha...glad you're enjoying them! As you've seen, I've already posted a TON of free videos on this channel. If you're looking for more in-depth and comprehensive content, check out some of my additional video lessons here: www.dominatethegmat.com/video-purchase/a-la-carte-topics/. Enjoy!
Why can’t we solve the problem by simply finding the average speed ((40+30)/2) and multiplying it by 7. This approach makes perfect sense but leads to the wrong answer.
Can`t we use the following formula, as we know, he has a one hour break on the way, and no break on the return: 40 * (t-1) = 30 * t => 40t - 40 = 30t 10t = 40 t = 4h => 120 Kilometers
Your formula implies that his time "out" is one hour less than his time returning, and we don't know that to be the case. The one-hour break for lunch is accounted for in changing 8 hours to 7 hours, his actual travel time. So stick with the setup I explained in this video to ensure a right answer on similar questions in the future.
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Thanks Brett for the question and solution !
You're welcome. Good luck on test day and don't hesitate to let me know if there's anything else we can do to help!
The way I solved it is by knowing that he will drive for 7 hours. He is going 40 and returning at 30 so you can estimate that he will be going 40 for around the first 3 hour then returning at 30 for the last 4 hour. You multiply 40 with 3 and 4 with 30 , you will get 120
That's a specific sense not everyone has it, your solution could solve the problem in less than 10 seconds, but not everyone familiar with this kind of troubleshooting ;)
Why can you stimate that he will be going 40 for around the first 3 hours?
I have done the same way
the way i solved it was:
40 * 7 hours = 280 /2 (round trip) = 140
30 * 7 = 210 /2 = 105
therefore the trip has to be less than 140 but more than 105. and i got the answer of 120
Total time= 7 hours = one round/30+one round/40, when you solve for one round it equals 120.
this helped so much thank you for the video
My pleasure. Glad it helped!
This a great problem. Thanks!
My pleasure, glad it helped!
I found the same result in 15 seconds just plugging in solutions, and usually the mid-solution is the one to start from; GMAT is not about finding the most correct way to solve a problem, it's about finding the smartest way
Yep, great approach! And that's what I teach in my non-standard GMAT math strategy lessons: www.dominatethegmat.com/video-purchase/a-la-carte-topics/gmat-strategies-non-traditional-math-techniques/
This is Physics, when I was in junior high school the formula is v = s.t, s=v/t, and t=v/s
V stands for Velocity
S stands for Speed
T stands for Time
he is correct in resolving the problem by looking for the t value, then apply that t value into the formula.
Maybe if you can speed up the process, that'd be great. Resolve one GMAT problem is like chasing the time :)
One of your strategies is to work backwards on problem solving questions if the answers are all numbers. Could you do that for this type of question? If so, could you explain how?
+Anthony DiDonato Yes, absolutely. And in fact that's probably the more efficient way to solve this problem! Start by assuming the correct answer is C. IF he drives out 145km into the desert at 40km/h, then it will take him 145/40 = 3.625 hours. Then on the way back it'll take him 145/30 = 4.833 hours. 3.625 hours + 4.833 hours + the 1 hour for lunch = 9.458 total hours, which is MORE than the 8 hours the problem says he spent. So answer choice C is wrong. It's also too many hours, which means 145km is too FAR, so answer choices D and E are also out. Now try A or B. If we try B, it'll take him 120/40 = 3 hours to drive out, then 120/30 = 4 hours to drive back, plus the 1 hour for lunch = 8 total hours. That works! Answer choice B.
+Dominate the GMAT Thank you!! this is really helpful! I definitely feel better about my chances after watching your videos.
am confused.why is it 7-t. I am confused
It's because the amount of time that he'll travel on the way back is different from the amount of time he'll travel going out, so we can't just let "t" be the time both directions. The problem gives us clues as to how to account for the difference in time. Specifically, we know he'll be traveling for 7 hours total (the 8 hour travel time minus the hour he stops for lunch). So we represent that as 7-t. For example, if his total travel time is 7 hours and it takes him 3 hours to go out, how long will it take him to return? Four hours, obviously. It's easy with real numbers. But since we don't know exactly how long it takes him to go out, be use the variable "t" to represent that.
Dominate the GMAT thank u my coach, u are amazing
I got confused because i was thinking it would be t-7, not 7-t.
I dont know if this method is applicable for all questions so let me know if this is limited in solving other qs.
But since distance is the same and since velocity is d/t, I just looked for the least divisible number of 30,40 which is 120, so I didnt calculate any time.
That's good reasoning for a question like this. Insightful! For anyone else reading this comment: Velocity is NOT tested on the GMAT, so focus on learning GMAT-specific math and reasoning strategies.
The d2 being 30(7 - t) although confusing, does work. I've accepted this...
Learn the methodology and apply it on test day. Whether you fully understand the logic or not, it'll get you a right answer. Means to an end!!
Hi Sir,
Thank you so much for this video. You are great, truly.
Thanks for taking the time to say so. Glad you found it helpful!
On the way back from the trip is it okay to use 30(t-1)?
No, because that would mean that he's traveling one less hour on the way back than on the way out, but that's not what the problem is saying. Their times are respective to the total eight hours (minus the hour for lunch on the way back in the case of the return trip), not relative to each other.
Dominate the GMAT thanks a lot.
Thanks for your videos. I have an observation: the distance drove was two times the same distance, not only one way, so the correct answer should be 240, right?
That would be the total distance for the entire round-trip. However, the question only asks for how far Steve can drive "into the desert," meaning only the "out" portion of the trip.
Why is the returning time 7-t? Sorry for this silly question.
"t" represents the amount of time it takes Steve to drive out into the desert. The amount of time for his return trip will be different since his rate is different, but we still want to represent it in terms of "t" so that we only have one variable. The best way to do that is to simply subtract "t" -- the amount of time he's already traveled going out -- from the total trip time; the difference is his return time. So what is the total trip time? Well he spends 8 hours total away from home, but an hour of that is sitting still for lunch. So the actual travel time is 8 - 1 = 7 hours. That's why the return time is (7-t).
@@dominatethegmat Well, "spending eight hours away from home including a one hour lunch break". Is it only during returning?
Also, I thought that one hour of lunch break was included in that eight hours. So, if that's included, why was it substracted?
@@shafiabdullahhauque7933 The time you're solving for is travel time, so you don't need to account for the one hour for lunch. It doesn't matter when the lunch break happens (i.e. whether the lunch break happens on the way out, before returning, or on the return trip is irrelevant), it simply needs to be subtracted from the 8 hours.
Easiest way to solve this problem is
Speed1*Speed 2 /Speed 1 + Speed 2 * Total time taken.
I tried to solve this question by using a different method and I couldn't get a right answer. R=40kph+30kph=70; T=7; D=2y . Given that R*T=D, I found y=245. I am not sure why my formula is incorrect.
You can't aggregate everything that way. Since it's a round-trip situation where the rate and time is different going and coming, you have to treat each individually. At no point is Steve going 70mph, so you can't use that as his collective rate over the entire trip.
It wants to know how far he can "drive into the desert". So you wouldn't count the distance traveled on the trip back. You can take his average speed which would give you 35km/h. All you need to do is take half of the total distance. D = (35 km/h)(7h) = 245
245/2 = 122.5
The answer is B
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RAHUL Sahni Hahaha...glad you're enjoying them! As you've seen, I've already posted a TON of free videos on this channel. If you're looking for more in-depth and comprehensive content, check out some of my additional video lessons here: www.dominatethegmat.com/video-purchase/a-la-carte-topics/. Enjoy!
Why can’t we solve the problem by simply finding the average speed ((40+30)/2) and multiplying it by 7.
This approach makes perfect sense but leads to the wrong answer.
Эмиль Мустафаев You can, but your calculation of average rate is wrong. Use this formula and try again: Average Rate = Total Distance / Total Time.
Can`t we use the following formula,
as we know, he has a one hour break on the way, and no break on the return:
40 * (t-1) = 30 * t =>
40t - 40 = 30t
10t = 40
t = 4h
=> 120 Kilometers
Your formula implies that his time "out" is one hour less than his time returning, and we don't know that to be the case. The one-hour break for lunch is accounted for in changing 8 hours to 7 hours, his actual travel time. So stick with the setup I explained in this video to ensure a right answer on similar questions in the future.