on a gmat pratcice test I rean into the following quest:

A cerain basket contains 10 apples, 7 are red, 3 are green. If 3 different apples are to be selected random from the basket, what is the probability that 2 of apples will be red & 1 will be green?

The answer states 21/40

I am having trouble finding how to get that number.. Please help

There are three ways we can get two reds and a green:

RRG
RGR
GRR

We calculate the probabilities of each of these and then we add them.

FOr RRG:

Probability of first R is 7/10
Probability of second R is 6/9
Probability of G is 3/8
When we multiply these three terms together we get 7/40.

For RGR:
R : 7/10
G: 3/9
R: 6/8
Product of the three is again 7/40

For GRR:
G: 3/10
R: 7/9
R: 6/8
Product of the three is again 7/40

7/40 + 7/40 + 7/40 = 21/40.

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