A boy is mowing a rectangular lawn 40ft long and 30ft wide. He has cut all of it except for a rectangle that is 20ft long and 15ft wide. What fractional part of the lawn remains uncut?

Question

I need helping figuring out how to solve this. My answer sheet says its 1/4 but I don't know how to solve for it. I need to know how to solve this problem. Please explain, thank you.

Answer 1

A = 40 * 30
A = 1,200 square feet

A = 20 * 15
A = 300 square feet uncut

300/1200 = 3/12 = 1/4