10 different names are put into the computer and one of the name is Colin.

a) On Saturday, the computer chooses 2 names at random. The computer is set so the same name *can* be chosen twice. What is the probability that Colin is chosen at least once?

b) On Sunday, the computer is set so that the same name *cannot* be chosen twice. Work out the probability that Colin is chosen.

Guest Mar 19, 2020

#1**0 **

a) Colin's name can be chosen on the first try but not on the second: (1/10) x (9/10) = 9/100

or his name can be chosen on the second try but not the first: (9/10) x (1/10) = 9/100

or his name can be chosen on both tries: (1/10) x (1/10) = 1/100

The answer is the result of adding these three values.

b) Colin's name can be chosen on the first try but not on the second: (1/10) x (9/9) = 1/10

or his name can be chosen on the second try but not the first: (9/10) x (1/9) = 1/10

Again, the answer is the result of adding these two valus.

geno3141 Mar 19, 2020