A common denominator for 2/5 is 4/10 because 2/5 times the denominator and numerator by 2 is 4/10
And the common denominator for 1/2 is 5/10 because 1/2 times the denominator and numerator by 5 is 5/10
So the equivalent denominators for both fractions is 4/10 and 5/10