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 take the second crew to finish cleaning the building?

1. 👍 2
2. 👎 1
3. 👁 1,788
1. 1/8-1 hour
2/8- 2 hours

2/8+1/10x=1
1/10x=6/8
x=7.5 hrs

1. 👍 5
2. 👎 2
2. let the work to be done be 1 unit

rate of first crew = 1/8
job done by first crew in 2 hours = 2(1/8) = 1/4
job left to be done = 1 - 1/4 = 3/4

rate of second crew = 1/10
time needed for 2nd crew to finish
= (3/4) / (1/10)
= 30/4 hrs or 7.5 hrs

1. 👍 5
2. 👎 0

Similar Questions

1. math

One pipe fills a storage pool in 20 hours. A second pipe fills the same pool in 15 hours. when a third pipe is added and all three are used to fill the pool , it takes only 6 hours. Find how long it takes the third pipe todo the

2. statistics

The Information Systems Audit and Control Association surveyed office workers to learn about the anticipated usage of office computers for personal holiday shopping. Assume that the number of hours a worker spends doing holiday

3. math

Suppose that the time (in hours) required to repair a machine is an exponentially distributed random variable with parameter λ (lambda) = 0.5. What's the probability that a repair takes less than 5 hours? AND what's the

4. Math

A person walks on the building.He slips 1m for every 5m he climbs. If the building is 53m high and he takes 5 seconds to climb 1m. Find the total time taken by him to get on the top of the building.

1. math

Three water pipes are used to fill a swimming pool. The 1st pipe alone takes 8 hours to fill the pool, the 2nd pipe alone takes 12 hours to fill the pool, and the 3rd pipe takes 24 hours to fill the pool. If all 3 pipes are opened

2. Linear Algebra

A hospital performs 3 types of operations. The first type takes 30 minutes, and they charge \$500 for it. The second type takes 1 hour, and they charge \$750 for it. The third operation takes 2 hours, and they charge \$1000 for it.

3. algebra

A man flies a small airplane from Fargo to Bismarck, North Dakota --- a distance of 180 miles. Because he is flying into a head wind, the trip takes him 2 hours. On the way back, the wind is still blowing at the same speed, so the

4. maths

8 cleaners can clean an office block in 3 hours. If two cleaners are off ill,how long will it take the rest to clean the block.

1. 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

2. math

a person was climbing on a building. He slips 1 m for every 5 metre he climbs up. If the building is 53 m high and he takes 5 seconds to climb 1 metre find the total time taken by him to get on the top of the building.

3. help making equations

Superbats, Inc., manufactures two different quality of wood baseball bats, the Wallbanger and the Dingbat. The Wallbanger takes 8 hours to trim and turn on a lathe and 2 hours to finish it. It has a profit of \$17. The Dingbat

4. math

Amy can clean the house in 7 hours. When she works together with Tom, the job takes 5 hours. How long would it take Tom, working by himself, to clean the house?