Working alone, Dan can sweep a porch in 15 minutes. Alberto can sweep the same
porch in 11 minutes. If they worked
together how long would it take them?

It will take them 6.35 minutes

Step-by-step explanation:

The question can be solved when you know how much of the job can be done in minutes.

Therefore if Dan can do the job in 15 minutes he will be to sweep 1/15 of the porch in 1 minutes. Alberto can do the same job in 11 minutes, in 1 minutes he will do 1/11 of the job.

let

a = combined time together

1/15 + 1/11 = 1/a

(11 + 15)/165 = 1/a

26/165 = 1/a

cross multiply

26a = 165

divide both sides by 26

a = 165/26

a = 6.34615384615

a ≈ 6.35 minutes

It will take them 6.35 minutes

twenty-six miles over two gallons because the proportion for the original 13 miles to one gallon would be written 13/1 and, doing the same thing to the top and bottom, i multiplied by 2 and got 26/2