Question

Michael's lawn mower had 3/8 of a gallon of gasoline in the tank. He started mowing and used all of the gasoline. He put 4/10 of a gallon of gasoline in the tank. After he mowed, 2/4 of a gallon was left in the tank. ​What was the total amount of gasoline Michael used?

Answer 1

11/40 of a gallon

Explanation:

The amount of gasoline in the tank of lawn mower = 3/8 of a gallon

Then he put the amount of gasoline in the tank = 4/10 of a gallon

The total amount of gasoline filled in the tank = 3/8 + 4/10

= 3/8 + 2/5

= 15+16/40

= 31/40

The total amount of gasoline filled in the tank = 31/40

The amount of gasoline left in the tank after mowing = 2/4

Total amount of gasoline Michael used = 31/40 - 2/4

= 31-20/40

= 11/40 of a gallon

Alternatively, you can follow this method:

Total amount of gasoline Michael used = 3/8 + (4/10 - 2/4)

= 3/8 + (2/5 - 2/4)

= 3/8 + ( 8-10/20)

= 3/8 + (-2/20)

= 3/8 + (-1/10)

= 3/8 - 1/10

= 30-8/80

= 22/80

= 11/40 of a gallon

Total amount of gasoline Michael used = 11/40 of a gallon