Question 1208629
We will use complementary counting. This means we want to find the probability that 0 or 1 of their children have the trait.
The probability of none of their children having the trait is {{{(3/5)^5}}}, since the probability for an individual child is {{{1-2/5=3/5}}}, and there are 5 of them.
The probability of exactly 1 of their children having the trait is {{{5*(2/5)*(3/5)^4}}}. The probability of a child having the trait is {{{2/5}}}, and the probability of the other 4 not having the trait is {{{(1-2/5)^4=(3/5)^4}}}. The child with the trait could be any of the 5, so we multiply by 5 to account for that.
So in total, the probability of 0 or 1 of their children having the trait is {{{(3/5)^5+5*(2/5)*(3/5)^4}}}, or 0.33696. Since that is the probability of there <b>not</b> being at least 2 children having the trait, the answer is 1-0.33696=0.66304, which rounds to 0.663.