Question

Which is the highest common factor of 40 and 60?

Answer 1

Factors of 40 = 1, 2, 4, 5, 8, 10, 20, 40
Factors of 60 = 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60.
20 is the highest common factor of 40 and 60.

Number inside the blue circle are factors of 60.
Numbers inside the red circle are factor of 40.
Numbers inside the shaded region are common factors and highest among them is 20, so is the highest common factor.