LCM (least common multiple)
The multiples of 4 is: 2 x 2
The multiples of 10 is: 2 x 5
In GCF, you multiply the common factors ONLY, but for the LCM, you need to multiply ALL the numbers.
The number 2 has a pair intersecting the multiples of 4 and 10, so you need to write it down only once, but the other 2 doesn't have a pair, so you should write it down.
So 2 x2 x 5
4x5=20
Hope this helped!