Jeff had $20. He spent 1/8 of his money on lunch and 2/5 of his money at the movies. How much money does Jeff have left?

First, multiply 20 by the given fractions

20*1/8=2.5
20*2/5=8
Add the two together to get the total amount of money Jeff spent, 10.5, then subtract 10.5 from 20 to get the total amount he has left, 9.5