Math

A roofing crew can roof a house in 10 hours. If a second crew was added, the job would take 6 hours. How long would it take the second crew to roof the house alone?

1. 👍 0
2. 👎 0
3. 👁 70
1. Working together is like resistors working in parallel:

t1*t2 / (t1 + t2) = 6,
10t2 / (10 + t2) = 6,
Cross multiply:
10t2 = 60 + 6t2,
10t2 - 6t2 = 60,
4t2 = 60,
t2 = 60 / 4 = 15 h.

1. 👍 0
2. 👎 0
posted by Henry

Similar Questions

1. math

A library crew can shelve books in six hours. Another crew can do the job in four hours. If the first crew begins and is joined by the second crew one hour later, how many hours will it take to finish the job?

asked by jessica on July 26, 2011
2. MATH NEED HELP!

I have four questions in one. 1. A library crew can shelve books in six hours. Another crew can do the job in four hours. If the first crew begins and is joined by the second crew one hour later, how many hours will it take to

asked by Leanne on August 10, 2011
3. math

It takes 8 hours for one crew to clean an office building. It takes a second crew 10 hours to clean the same building. If the first crew works 2 hours and leaves and the second crew takes over to complete the job, how long will it

asked by Christos on October 22, 2016
4. math

A boat's crew rowed 12 miles downstream, with the current, in 1.5 hours. The return trip upstream, against the current covered the same distance, but took 4 hours. Find the crew's rowing rate in still water and the rate of the

asked by sam on April 24, 2010
5. Algebra

One crew can frame a single story house in 7 days, while a second crew can do it in 5 days. how long will it take to frame a single house if the second crew arrived 2 days after the first. Im having problems setting it up with the

asked by Leonard on April 12, 2016
6. Math

A crew is made up of 8 men; the rest are women. 66 and 2 thirds of the crew are men. How many people are in the crew

asked by Anonymous on May 1, 2019
7. help asap plz

A 15-person road crew is scheduled to finish repairing a highway in 12 days. On the morning of the fifth day, several new workers join the crew and, together, they complete the remaining repairs in 6 days. How many new workers

8. Algerbra

A boat's crew rowed 10.5 miles downstream, with the current, in 1.5 hours. The return trip upstream, against the current, covered the same distance, but took 3.5 hours. Find the crew's rowing rate in still water, and the rate of

asked by Ali on April 10, 2013
9. algebra

A boat's crew rowed 13.5 miles downstream, with the current, in 1.5 hours. The return trip upstream against the current covered the same distance, but took 4.5 hours. Find the crew's rowing rate in still water and the rate of the

asked by tiara on December 15, 2010
10. Algebra

A boat's crew rowed 7.5 downstream,with the current, in 1.5 hours. The return trip upstream against the current,covered the same distance,but took 2.5 hours. Find the crew's rate in still water and the rate of the current.

asked by Anna on March 27, 2012

More Similar Questions