# Math

posted by Gary

A man can do a certain task in 21 hours, another man can do the task in 28 hours and a boy can do the task in 48 hours. Find how long it will take to do the task if all three work.

1. Arora

Try figuring out how much of the task each man can do in one hour, as a fraction.

You can use that to find out the work done in an hour if all three work together, and thus the amount of time it will take.

2. Melvin

Man 1/21 other man 1/28 boy 1/48
Man’s rate other man’s rate boy’s rate
1/21 1/28 1/48
Let x be the number of hours it will take all three
Combined rate = 1/x
1/21 + 1/28 + 1/48 =
LCD = 28, 224
1344 / 28, 224 + 1008 / 28, 224 + 588 / 28, 224
= 2 940 / 28, 224 or 735 / 7056
1/x = 735/7056
Cross multiply
735x = 7056
x = 7056/735
x = 9.6 or 9 hours and 10 minutes

## Similar Questions

1. ### college algebra

Find the time for two people working together to complete half a task if it takes them 8 hours and 10 hours to complete the entire task working individually.
2. ### college algebra

Find the time for 2 people working together to complete half of a task if it takes them 8 hours and 10 hours to complete the entire task working individually. Thank you!!!
3. ### Radical and Rational exponents

Estimate how long it takes you to complete a task of your choice (house cleaning, mowing, etc.) in a given week. Suppose that Joe is slower than you at the given task and takes three times as long as you do. If you work together, how …
4. ### math

it takes janet 9 hours to do a task and it take jancie 10 hours to do the same task how long will it take both of them to do the task together
5. ### math

if wayne completed a task in one hour and sarah completed a task in two hours, how long will they take if they work together?
6. ### Math/Management

Ten jobs are to be completed by three workers (Sam, Joy, and Kelly) during the next week. Each person works a 40-hour week and is paid an hourly rate: Sam, Joy, and Kelly earn \$11, \$13, and \$14 per hour, respectively. Union rules require …
7. ### math

If A and B work together,they can finish a task in 2 hours. If they do the task separately, B can finish 3 hours earlier than A can. Find the time required for B to finish the task alone.
8. ### Algebra

Working​ together, Sarah and Jeff can do a task in 6 hours. Jeff uses a motorized cart to do the​ task, whereas Sarah uses a pushcart. If each person does the task without the help of the​ other, it takes Sarah twice as long …
9. ### algebra

A can do certain task in 8 hours, B in 10 hours and C in 12 hours. How long will it take to do the task if A and B work 1 hour and then A and C finish the task?
10. ### algebra

A man can do a certain task in 21 hours, another man can do the task in 28 hours and a boy can do the task in 48 hours. Find how long it will take to do the task if all three work.

More Similar Questions