First what you need to do is give these fractions common denominators. 2/5 and 1/2 can be converted to 4/10 and 5/10 (2*2/5*2, 1*5/2*5). Now, just subtract 4 4/10 and 1 5/10. Subract the whole numbers first (4-1=3) and then the fractions (4/10-5/10= -1/10)You come out with 2 9/10.