Find a common denominater: for 5 and 8 it would be 40: 2/5(8/8)=16/40, 1/8(5/5)=5/40. Add the numerators (in a subtraction problem subtract instead of adding): 16/40+5/40=21/40. Simplify if possible. For mixed number problems make them improper fractions then solve. :) hope this makes sense
