For this problem, you can either turn the fractions into decimals or same denominator fractions.
So -2/5 = -0.4 OR -4/10
And 1/2 = 0.5 OR 5/10
Because -4/10 is negative, you could even change this equation to : 5/10 - 4/10
All that did was switch the order. You can either think of this equation as 5/10 minus 4/10 OR the original way : 4/10 plus a positive 5/10.
The answer would be 1/10.