I4.4 If $c$ boys were all born in June 1990 and the probability that their birthdays are all different is $\frac{d}{225}$, find $d$
$\mathrm{P}(3$ boys were born in different days $)=1 \times \frac{29}{30} \times \frac{28}{30}=\frac{d}{225}$ $d=203$