Question

One crew can seal a parking lot in 10 hours and another in 14 hours. how long will it take to seal the parking lot if the two crews work together?

Answer 1

Suppose that all work that has to be done is 1. Then:

• One crew can do this work in 10 hours. This means that they will do
  `(1)/(10)` per hour.
• Another crew can do this work in 14 hours.This means that they will do
  `(1)/(14)` per hour.
• Both crews together will do
  `(1)/(10)+(1)/(14)=(7+5)/(70)=(12)/(70)=(6)/(35)` per hour.

If together they can do
`(6)/(35)` per hour, then for all work they will spend

`(1)/((6)/(35))=(35)/(6)=5(5)/(6)` hours or 5 hours 50 minutes.

Answer: 5 hours 50 minutes.