PSL4#28

$|p|=\dfrac{1500}{4}=375\\ |g|=\dfrac{1500}{5}=300\\ |b|=\dfrac{1500}{3}=500\\~\\ \text{let $X$ be the set with none of the above}\\ |X| = 1500 - |p \cup g \cup b|\\~\\ \text{The smallest value of $|X|$ is obtained if the 3 sets above don't intersect}\\ \text{In this case $|X|=1500-375-300-500 = 325$}$