How do you find LCD for 3 numbers?

Answer 1

The same as with two.
Example: 30, 42, 60
Factor them.
2 x 3 x 5 = 30
2 x 3 x 7 = 42
2 x 2 x 3 x 5 = 60
Combine the factors, eliminating duplicates.
2 x 2 x 3 x 5 x 7 = 420, the LCD