Help me check whether I'm correct the lcm of 15 and 18 is it 90
No, the least common multiple (LCM) of 15 and 18 is not 90.
To find the LCM, you need to consider the prime factorizations of both numbers.
The prime factorization of 15 is 3 * 5.
The prime factorization of 18 is 2 * 3 * 3.
To find the LCM, you take the highest power of each prime factor that appears in either number. In this case, you take 2, 3 (highest power of 3), and 5.
Therefore, LCM(15, 18) = 2 * 3 * 3 * 5 = 90.
So, your answer is correct. The LCM of 15 and 18 is indeed 90.