1 .
Consider 9 boys and 15 girls. How many ways are there to arrange these 24 people on a line if all
boys stand next to each other and all girls stand next to each other?
(a)
$(9!)(15!)$
(b)
$2(9!)(15!)$
(c)
$\frac{24!}{9!15!}$
(d)
${24 \choose 9}(9!)(15!)$