algebra word problem

[girlpower]

Working alone , Pierre can complete a job in 10 hours . Juan can do the same job in 8 hours. How long would it take them to complete the job if they work together?

 

[JeffM]

Working alone , Pierre can complete a job in 10 hours . Juan can do the same job in 8 hours. How long would it take them to complete the job if they work together?

You seem to have entirely the wrong idea. We are not here to do your homework problems for you. We are here to help you with problems in your doing your homework. We cannot do that if you do not show us your work, which does not mean some guess. Even if you do not know how to solve this problem because no similar problem is shown in your book or class materials, surely you have some ideas.

What fraction of the work can each do in an hour individually?

Does that give you any ideas for a next step?

 

[girlpower]

I don't have a similar problem to the one I am doing it's in a math placement exam packet. But help meeeeeeeeeeeeeeeeeeeeee!!!!!!!!!!!!!!!!!!!!!!

 

[Deleted member 4993]

I don't have a similar problem to the one I am doing it's in a math placement exam packet. But help meeeeeeeeeeeeeeeeeeeeee!!!!!!!!!!!!!!!!!!!!!!

Jeff asked you aquestion that you should be able to answer:

What fraction of the work can each do in an hour individually?

Answer that first then help will come....

 

[HallsofIvy]

When you have people or machines doing a job or pipes filling a tank, etc., the crucial point is that the rates add. If "Pierre can complete a job in 10 hours", what is Pierre's rate of work, in "jobs per hour"? If "Juan can do the same job in 8 hours", what is Juan's rate of work in "jobs per hour". So what is the rate of work of the two together?

 

[harpazo]

Work Word Problem

Working alone , Pierre can complete a job in 10 hours . Juan can do the same job in 8 hours. How long would it take them to complete the job if they work together?

1/8 = fractional part of the job by Juan

1/10 = fractional part of job by Pierre

Let x = number of hours to do the job together

1/8 + 1/10 = 1= x

Multiply each fraction by LCD 40x.

5x + 4x = 40

9x = 40


x = 40/9 hours

x = four and 4/9 hours.


Note: When I first solved the problem, I forgot to include x as part of the LCD.

 

[Deleted member 4993]

1/8+1/10=1/x

10+8 = 80x

18 = 80x

18/80 = x

9/40 = x

Another Method

8+10)/8*10 =

18/80 = 9/40

The answer is 9/40 hours.

9 hours, 13 minutes, 30 seconds

The above calculations are wrong!

Working alone , Pierre can complete a job in 10 hours . Juan can do the same job in 8 hours. How long would it take them to complete the job if they work together?

Let the number of hours working together = h

1/8 + 1/10 = 1/h → (5+4)/(40) = 1/h → h = 40/9 hrs = 4 hrs 240/9 min = 4 hrs 26 min 2/3*60 sec = 4 hrs 26 min 40 sec

 

[lookagain]

Working alone , Pierre can complete a job in 10 hours .
Juan can do the same job in 8 hours. How long would it take them to complete the job if they work together?

How should someone know if their answer is reasonable? The worker who works the slowest is the weakest link.

If there were two people who could each do the job in 10 hours, then they would take 5 hours to do it
together.

If there were two people who could each do the job in 8 hours, then they would take 4 hours to do it
together.


The answer for both of these people doing the one job together must lie in between four hours and five hours.

 

[harpazo]

Correction on Typo

The above calculations are wrong!



Let the number of hours working together = h

1/8 + 1/10 = 1/h → (5+4)/(40) = 1/h → h = 40/9 hrs = 4 hrs 240/9 min = 4 hrs 26 min 2/3*60 sec = 4 hrs 26 min 40 sec

Thanks for pointing out my error. I simply forgot
to multiply by 40x.