6 machines can do a job in 8 hrs.

5 machines con do a job in ?

Now think, will 5 machines take more than 8 hrs, or less? Of course more than 8 hrs since fewer machines are working.

So number of hours 5 machines will take =

8 * (\frac{6}{5})Basically, you need hours so given hours term i.e.

8 * \frac{6 machines}{5 machines} to get 9.6 hours.

We multiply by 6/5 to increase 8 since more hours are required.

It is actually a Variation question (Inverse Variation here) but it is just easier to think in terms of more/less.

Another e.g. 10 people make 5 chairs in a day. How many people do we need to make 12 chairs.

Simply multiply 10 (the number that you want to change) by 12/5 because you want to increase the number of people to make more chairs:

10 * (\frac{12}{5}) = 24 people

Yet another e.g. 10 people need 4 hours to complete a job. How many hours do 18 people need to complete the same job?

4 * (\frac{10}{18}) = 2.2 hrs

If there are more people, they will need fewer hours so multiply by 10/18 (not 18/10).

_________________

Karishma

Veritas Prep | GMAT Instructor

My Blog

Save $100 on Veritas Prep GMAT Courses And Admissions Consulting

Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.

Veritas Prep Reviews