a family has 5 children. What is the probability that at least one child is a girl?

50/50 they either are or they aren't.

No probability and no way to determine future. I know people with 6 girls and others with 5 boys. We were lucky, 2 + 2

The question isn't what is EACH child's odds are, but ONE out of FIVE (boy or girl isn't relevant). It's a terrible question, because so many factors are in play. You are better off flipping a coin 5 times.

Please [READ THIS], it explains basic statistics. From this you will be able to answer your question.

(The basic idea is to figure out what the chances of getting all 0's in a binary series, subtract that from 100% and you will get the probability of having at least one 1 in said binary series. For example if you flip a coin two times, there is a .5 chance that you will get heads on each toss, multiple those together and you will get a .25 chance you will get two heads, which means that there is a .75 chance that, if you toss two coins, you will get at least one tail.)

See the basic approach to this question must be:-
Find the probability that none of the child is a girl.
Substract this probability from the total probability to get your desired answer.
For further details , show your approach to the question.