Q: If n is a multiple of 5 and n=(p^2)q, where p and q are prime numbers, which of the following must be a multiple of 25?

A) p^2
B) q^2
C)pq
D)(p^2)(q^2)
E)(p^3)q




here's the theory approach:

the only two primes in n's prime box are p and q.
since 5 is prime, either p or q is 5. it's impossible to tell which one.
this is actually all you need: in order to guarantee a multiple of 25, you have to square both of these primes, because you don't know which one is 5.
only (d) does this.