What are the common factors of 20 and 50

2 and 5.

20 / (2) = 10, 10 / (5) = 2

50 / (2) = 25, 25 / (5) = 5

Factoring out 20, you'd get 2 • 2 • 5, because those numbers multiplied = 20.

Factoring out 50, you'd get 2 • 5 • 5, because those numbers multiplied = 50.

2 and 5 is the answer because those are the only prime numbers that will fit into them both without excluding one or the other from one number.