Question

A demolition crew can do a job in 10 days. Another demolition crew can do the same job in 15 days. How many days would it take the two crews to do the job if they work together?

Answer 1

6 days

Explanation:

In one day, one demolition crew:

One day =
`(1)/(10) x` with x = the entire job

Other demolition crew:

One day =
`(1)/(15) x`

Together, they do it in
`(1)/(10)x\\` +
`(1)/(15)x` =
`(3)/(30)x + (2)/(30)x = (5)/(30)x`
`= (1)/(6)x` in one day

So
`(1)/(6)x` x 6 = x

so it takes 6 days to complete the work together.