Assume that in a family, each child is equally likely to be a boy or a girl. A family with three children is chosen at random. The probability that the eldest child is a girl given that the family has at least one girl is
1
\(\frac{1}{2}\)
2
\(\frac{1}{3}\)
3
\(\frac{2}{3}\)
4
\(\frac{4}{7}\)