Question

Find the probability of each event. Answer IN FRACTION form.

A bag contains five real diamonds and five fake diamonds. If five diamonds are picked from the bag at random, what is the probability that all of them are real?

Answer 1

So the idea is that we want to find the total number of ways that we can pick 7 diamonds (real or fake) from the 12 diamonds.

So as you said, 12 choose 7 = 792

Now we need the total number of ways that we can satisfy that of the 7 we picked, exactly three are real, but this also means that four are fake.

So to choose 3 real from 5 is 5 choose 3 = 10

And to choose 4 fake from 7 is 7 choose 4 = 35

3x10/792= 350/792= 175/396