G9.4 There are 4 red balls and 3 black balls in a box. If 3 balls are chosen one by one with replacement, what is the probability of choosing 2 red balls and 1 black ball?
$\mathrm{P}(2$ red, 1 black $)=3 \times\left(\frac{4}{7}\right)^{2} \times \frac{3}{7}=\frac{144}{343}$