marijose wrote:

Im not surprized!

I dont want to be rude either but that is why I posted the question in the forum, I dont want to start studying something that isnt recommended by this comunity!.

Thanks for your comments Ill start with words translations in the comming days and see how it goes from there.

regards

Work Rate problems are based on two and only two concepts:

1. Rates are additive.

2. Work done = Rate * Time (much like Distance = Speed * Time)

(Remember, Rate of work is just the speed of doing work)

If I paint half a wall in an hour and if you paint half a wall in an hour, if we both work together on a wall, we will finish the wall in an hour.

If my rate of work is 1/2 wall/hour and yours is 1/2 wall/hour, our total rate of work is 1/2 + 1/2 = 1 wall/hour (that is what we mean by 'rates are additive')

Now, if the question is: How many walls will we paint together in 8 hours?

Work = Rate*Time

Work = 1*8 = 8 walls

Use these two concepts and you will be able to solve most questions.

The basic questions of work rate are of the following form:

If A, working independently, completes a job in 10 hours and B, working independently, completes a job in 5 hours, how long will they take to complete the same job if they are working together?

Since A completes a job in 10 hours, his rate of work is 1/10th of the job per hour. B's rate of work is 1/5th of the job per hour.

Their combined rate of work would then be 1/10 + 1/5 = 3/10th of the job per hour.

As we said before, Work done = Rate * Time

1 = 3/10 * T (because 1 job has to be done)

or T = 10/3 hours.

This implies that A and B will together take 3.33 hours to do the job.

Note: Time taken when A and B work together will obviously be less than time taken by A or B when they are working independently.

Note: Time is not additive. In the question above, you obviously cannot say that A and B will together take 10+5 = 15 hrs to complete the job. Working together, they will take less time than either one of them working alone takes.

Try using these two concepts to solve your work-rate problems... Post specific questions if issues arise...

_________________

Karishma

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