Question

What is the lcm of 16 and 20

Answer 1

The least common multiple is 2
16 1,2,4,8,16
20 1,2,4,5,10,20

Answer 2

LCM stands for 'Lowest Common Multiple' which basically means "what's the smallest number that has the numbers in its multiplication table, excluding 1."*

So, the only numbers that are LCMs of 16 and 20 are 2 and 4. The lowest one is 2, so that's your answer.

* It's actually a little more complex than that, but I guess that was the easiest way to put it.