Martha has $20 to spend and would like to buy as several calculators as possible along with the money. The calculators that she needs to buy are $4.50 each. How much money will she have left over after she purchases the greatest possible number of calculators?

Divide the $20 through $4.50 to ?nd out the number of calculators she can buy; $20 ÷ $4.50 = 4.444. She can buy 4 calculators. She doesn't have sufficient to buy a ?fth calculator. This means in which she has spent $18 on calculators since $4.5 × 4 = $18. To ?nd out how much she has left; subtract $20 and $18. The answer is $2.