7 = 7
8 = 2 * 2 * 2
9 = 3 * 3
10 = 2 * 5
It's like we're making a parts list with enough parts to make 7, 8, 9, or 10. In this case our parts list is 2 * 2 * 2 * 3 * 3 * 5 * 7 because that has enough parts to make either 7, 8, 9, or 10.
2 * 2 * 2 * 3 * 3 * 5 * 7 = 2520
Answer: The LCD is 2520.