You're undercounting in Case
2.
Case 1: All
3 prizes to different people =
5 ×
4 ×
3 =
60. This is correct.
Case 2:2 prizes to one person,
1 to another. Here's where the mistake is. You wrote
5 ×
1 ×
4 =
20, but you forgot that the prizes are DIFFERENT. You need to first choose WHICH
2 of the
3 prizes go to the same person.
For example, giving prizes {A, B} to Student 1 and prize {C} to Student 2 is a DIFFERENT outcome than giving prizes {A, C} to Student 1 and prize {B} to Student 2.So the
correct count is:
- Choose which
2 prizes go together:
C(3,2) =
3 ways
- Choose who gets the pair:
5 ways
- Choose who gets the remaining prize:
4 ways
- Total =
3 ×
5 ×
4 =
60Case 3: All
3 prizes to same person =
5. This is correct.
Adding up:
60 +
60 +
5 =
125. That matches answer
E!
Your missing piece was the
3 ways to select which pair of prizes goes together in Case
2. That accounts for exactly the
40 you were short (
60 -
20 =
40).
Answer: ESoumya_Pinjala
So I tried to solve it as
3 prizes go to diff people = 5*4*3
2 prizes go to same person and 1 to another = 5*1*4
3 prizes go to same person = 5*1*1
Adding up gives 85. But this is not the answer. Am I missing cases or is this approach wrong. I would like to understand to avoid mistake in the future