It takes two hours for a person X to mow the lawn. Y can mow the same lawn in four hours. How long (in minutes) will it take X and Y

Q. It takes two hours for a person X to mow the lawn. Y can mow the same lawn in four hours. How long (in minutes) will it take X and Y, if they work together to mow the lawn?

(A) 60

(B) 80

(C) 90

(D) 120

Ans: 80

Solution:

Work done by X in 1 hour=1/2

Work done by Y in 1 hour=1/4

Work done by X and Y together in 1 hour

=1/2+1/4=3/4

∴ Total time to complete mowing of lawn

=43 hour =43×60=80 min