When we have j divisible by 12 and 10, since 2 is a prime factor of both 12 and 10, we only need to count it once (not separately). Let's pretend the question was instead "If j is divisible by 24 and 20..." How would we set up the prime factors of j? We have 24 (2, 2, 2, 3) and 20 (2, 2, ...