Question by falcon handsome - Discuss with MathYouLike

falcon handsome moderators

09/03/2017 at 12:34

Let the answer be k . We count the total number of paris of students were on duty together in the k days. Since every pair of students was on duty together exactly once, this is equal to \(C^{15}_2\) x 1 = 105. On the other hand, since 3 students were on duty per day, this is also equal to \(C^3_2\) x k = 3k. Hence 3k = 105 and so k = 35

double counting

List of answers

Ace Legona 09/03/2017 at 18:03

What did you try ?
Pham Hoang Nam 18/04/2017 at 21:33

What did you try ?
phanhuytien 11/08/2017 at 20:59

What did you try?
Trần Nhật Dương 24/06/2017 at 21:22

What did you try?
ảo ảnh 01/06/2017 at 13:52

i don't understand !
Đỗ Duy Mạnh 11/04/2017 at 11:11

What did you try ?

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