# Solved (Free): Suppose that the probability of parents having a child with blond hair is 1/4. If there are 6 children in the family

#### ByDr. Raju Chaudhari

Mar 15, 2021

Suppose that the probability of parents having a child with blond hair is 1/4. If there are 6 children in the family, what is the probability that half of them will have blond hair?

#### Solution

Let $X$ denote the number of children with blond hair. Given that $n=6$, $p=1/4$. $X\sim B(6, 1/4)$.

The probability mass function of $X$ is
 \begin{aligned} P(X=x) &= \binom{6}{x} (0.25)^x (1-0.25)^{6-x},\\ &\quad x=0,1,\cdots, 6 \end{aligned}

The probability that half of them will have blond hair is

 \begin{aligned} P(X=3) &= \binom{6}{3} (0.25)^{3} (1-0.25)^{6-3}\\ &= 0.1318 \end{aligned}