我想問probability幾時要係個分數乘個整數呢?例如呢條數:
Stem(tens) Leaf(units)
1 2 5 5 7 8
2 4 4 4 4 5 6 7 9
3 2 2 2 2 5 5 5 6 8
4 2 3
Find the probability that the mean score of the two students is the same as the mean score of the 24 students. (mean score is 28)
Ans: Let x and y be their marks.
(x+y)/2=28
x+y=56
Possible combinations: (18,38) (24,32), (27,29)
Probability:
2x(1/24x1/23)+2x (4/24x4/23)+2x (1/24x1/23)
=3/46
為什麼要在分數之前乘一個整數2 呢?