One crew can seal a parking lot in 6 hours and another in 10 hours. How long will it take to seal the parking lot if the two crews work together?

Question

One crew can seal a parking lot in 6 hours and another in 10 hours. How long will it take to seal the parking lot if the two crews work together?

Answer 1

1/6 + 1/10 = 1/T

multiply by 30T

5T + 3T = 30

8T = 30

T = 30/8 = 15/4 = 3.75 =

3 3/4 hours working together

Answer 2

Let x = number of hours it takes if both crews work together

1/10 = amount of the job done by the first crew in 1 hour

1/6 = amount of the job done by the second crew in one hour

1/x = amount of the job done by both crews in 1 hour if they work together

1/10 + 1/6 = 1/x

Multiply both sides by the LCD, 30x:

3x + 5x = 30

8x = 30

x = 30/8 hours = 3.75 hours