A couple have 3 children, 2 affected with a genetic disorder and 1 unaffected.?

Question

How many different birth orders are possible in which 2 of the children are affected and 1 is not?

Answer 1

Only three different birth orders for one unaffected. The reason that it isn't six different birth orders is that it doesn't matter which of the the affected children is in which place. So the unaffected one can either be first, second, or third.

In the first answer you received, if the unaffected one is letter a, then abc and acb would count as one order instead of two because they are both unaffected, affected, affected.

Answer 2

6different birth orders

abc, cba,acb,bca, cab,bac