Hi! Because the question asks about “at least” 1 junior, so using your method you have to consider the number of combinations for 1 junior + 2 juniors + 3 juniors + 4 juniors 😀
@@yimakesiteasy Thank You very much! I really like your channel, and your website is very helpful! I recently did an exam with the aid of your website! I'll report back with the results!
hey man, the reason the 5 and the 4 are not factorials is because there are only two seats for both girls. So any one of the 5 girls can sit in the first seat, then any of the remaining 4 can sit in the next seat. That gives you the number of possibilities for the first 2 seats. The 7! is for the rest of the seats :). Tell me if you need more help.
Hello, I assume you’re talking about the steps I did in 8:45! If you see the formula for nPr in 5:43, you can see the denominator/bottom of fraction is the top number in P minus the bottom number in P (in this case, it’s 8P5, so 8-5 = 3, so denominator is 3!). When I have the numerator as 8!, and denominator as 3!, you can visualise it: 8! = 8*7*6*5*4*3*2*1 3! = 3*2*1 You can notice we can cancel the 3*2*1 from top and bottom (similar to how we can cancel 2 in (2*3)/2 to get just 3). 3*2*1 is 3!, so I don’t need to write out all of the values, and I know I can just take away values from the number in denominator to 1. I understand it’s a bit confusing; do you need another explanation?
Hello! For 8:47 I was wondering when doing my add maths paper do I have to write out the permutation like 8P5 = 8x7x6x5…/3x2x1 or can I immediately write 8P5 = 6720 if I use my calculator
Hello there! Generally if the question is one mark, you can just put 8P5, but if the question is worth two or three marks, it's better to write out 8P5 = (8*7*6*5*...)/(3*2*1) = 6720 so the examiner can see your working. But what I usually do is i just write all my working out to: 1) Avoid losing any working marks, 2) So it's easier to check my work and to find any errors
Hello, it does. I grouped O & R together, and before the 6!, I multiplied it by 2 so it accounts for the arrangement where O is before R and R is before O😀. Does that make sense?
CIE IGCSE Add Maths time stamps:
Permutations & Combinations - Basics: 00:18
Permutations & Combinations - Examples: 08:20
Hey! Thanks for all your videos, they really helped me learn add math, and they're great! Keep it up man :)
Glad you find them useful! Let me know if you need any help!!
the last question part c why cant we do 4C1 to find the 1 junior multiply it by 6C4???
Hi! Because the question asks about “at least” 1 junior, so using your method you have to consider the number of combinations for 1 junior + 2 juniors + 3 juniors + 4 juniors 😀
Thanks, Sir.
Hope it helps! :)
Hey! what keywords should you look out to easily determine a combination or a permutation question?
Hello! The keywords include "only", "at least", "equal to", "not", "(no) restriction"
@@yimakesiteasy Thank You very much! I really like your channel, and your website is very helpful! I recently did an exam with the aid of your website! I'll report back with the results!
Your support means a lot to me! Well done with your exam, I’m sure you aced it :)
Thank u man
Hi, In question 3 10:56 I don’t understand why it was 5x4x7! And not 5!x4!x7! ? Also I your website and videos are so helpful!
hey man, the reason the 5 and the 4 are not factorials is because there are only two seats for both girls. So any one of the 5 girls can sit in the first seat, then any of the remaining 4 can sit in the next seat. That gives you the number of possibilities for the first 2 seats. The 7! is for the rest of the seats :). Tell me if you need more help.
You're exactly right!
hi, why did u cancel put the 3! factorial in 8!/3!
Hello, I assume you’re talking about the steps I did in 8:45!
If you see the formula for nPr in 5:43, you can see the denominator/bottom of fraction is the top number in P minus the bottom number in P (in this case, it’s 8P5, so 8-5 = 3, so denominator is 3!).
When I have the numerator as 8!, and denominator as 3!, you can visualise it:
8! = 8*7*6*5*4*3*2*1
3! = 3*2*1
You can notice we can cancel the 3*2*1 from top and bottom (similar to how we can cancel 2 in (2*3)/2 to get just 3).
3*2*1 is 3!, so I don’t need to write out all of the values, and I know I can just take away values from the number in denominator to 1.
I understand it’s a bit confusing; do you need another explanation?
@@yimakesiteasy ohh, thank you for the explanation! it’s more clear now ^•^
Awesome! Feel free to ask any more questions if you have any :)
Hello! For 8:47 I was wondering when doing my add maths paper do I have to write out the permutation like 8P5 = 8x7x6x5…/3x2x1 or can I immediately write 8P5 = 6720 if I use my calculator
Hello there! Generally if the question is one mark, you can just put 8P5, but if the question is worth two or three marks, it's better to write out 8P5 = (8*7*6*5*...)/(3*2*1) = 6720 so the examiner can see your working. But what I usually do is i just write all my working out to: 1) Avoid losing any working marks, 2) So it's easier to check my work and to find any errors
Hey, in the first question your answer doesn't account for the possibility that OR are arranged with R being before O
Hello, it does. I grouped O & R together, and before the 6!, I multiplied it by 2 so it accounts for the arrangement where O is before R and R is before O😀. Does that make sense?
@@yimakesiteasy thank you (for the quick response and the clear explanation and the great channel)
@@devanshpatil1065 thank you for your support 🙏
Hello there in question 19:00 b) they didnt say 3 seniors only so it can includw 4 5 or even 6 seniors am I wrong?
Hello, it is 3 seniors only. I should’ve specified “only”. Thanks for pointing it out!
@@yimakesiteasy yeah thx man but if the question was written as it in the video which way should u solve it
Generally if the answer may involve 4 or 5 or 6 or more seniors, the question will be “more than 2 seniors” or “greater than or equal to 3 seniors”