Twin​ brothers, Billy and​ Bobby, can mow their​ grandparent's lawn together in 98 minutes. Billy could mow the lawn by himself in 25 minutes less time that it would take Bobby.

Question

Twin​ brothers, Billy and​ Bobby, can mow their​ grandparent's lawn together in 98 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

Knowns

1. Together it takes them 98 minutes
2. Billy's relation to Bobby's mowing rate

We can set up system of equations because there is a related rate/time involved

Bobby's rate as a function: x

Billy's rate as a function: x-25

I got to these equations because it's implied the amount of time it takes billy to mow grass is based on how long it takes Bobby. So I have Bobby's rate as x.

When it is asking how long it would take Bobby to mow the lawn by himself, they are asking for x. We can set up a equation with all given information as

98=(x-25)+x

OR

98=2x-25

Solving for x we get

x=61.5

The answer is 61.5 minutes.