Question 316450
Let's look at it the other way.
What is the probability that they will have all boys?
P(B,B,B,B,B,B)=(1/2)(1/2)(1/2)(1/2)(1/2)(1/2)=1/64
P(all boys)+P(not all boys)=1
P(not all boys)=1-P(all boys)
P(at least 1 girl)=1-1/64=63/64.