Question

1) Working alone, Beth can tar a roof in 151

hours. Mike can tar the same roof in 14

hours. If they worked together how long

would it take them?

A) 7.24 hours B) 6.07 hours

C) 6.22 hours D) 7.12 hours

E) 5.81 hours

Answer 1

A) 7.24 hours

Explanation:

The together rate is the sum of each separate rate.

In this problem:

Beth's rate is 1/15(suppose there was a small typing mistake there, with 151 none of the options are correct).

Mike's rate is 1/14

The together rate is 1/x

Then

We want to find x.

`(1)/(15) + (1)/(14) = (1)/(x)`

15*14 = 210. So

`(14 + 15)/(210) = (1)/(x)`

`(29)/(210) = (1)/(x)`

Cross multiplication

`29x = 210`

`x = (210)/(29)`

`x = 7.24`

So the correct answer is:

A) 7.24 hours