Billy and Bobby mowing the lawn together

Question

billy and bobby, can mow their grandparents lawn together in 119 minutes. Billy could mow the lawn by himself in 25 minutes less time that it would take Bobby. How long would it take Bobby to mow the lawn by himself?

Answer 1

119/x + 119/(x-25) = 1

 

119(x-25) + 119x = x(x-25)

 

119x - 2975 + 119x = x² -25x

 

x² -263x + 2975 = 0

 

x ≈ 251 minutes for Bobby

 

226 minutes for Billy

 

Check answer

 

119/251 + 119/226 = 1

 

1=1