Question

what is the rhee and pamela are two of the five members of band. every week the band picks 2 members at random to play on their own for five minutes. what is the probability that rhee and pamela are chosen this week.

Answer 1

First you need to count the number of different two people groups you can make.

That is 5x4/2 = 10 different groups (this is because you can choose the first member from 5 different persons and the second member from 4 different persons, which makes 5 x 4; then you realize that in that way every couple is counted twice and so you have to divide by 2).

If you do not see that, you can count in this way. Identify every person with one letter: a, b, c, R and P

you can do these different two people groups:

ab
ac
aR
aP

bc
bR
bP

cR
cP

RP

Thos are the ten different groups.

Rhee and Pamela is one group, so the probability of chosing it is

1/10 = 0.1