Its about sat

Question

cathy can do a job in 8 hours while danny can do the same job in 6 hours . If cathy and danny work together for three hours , what fraction of job is left to be finished. 

 

Thx in adv .

Answer 1

If the work together the will require x hours to do the job where

(1/8) + (1/6) = (1/x)

 

x = 24/7 hours

 

What part of 24/7 does 3 represent?

3/(24/7) = 21/24 = 7/8

 

Therefore 1/8 of the job will be unfinished.

 

The reason that work problems always seem to involve reciprocals is because the reciprocals are rates.

For example: 1/8 means Cathy works a rate of job/8 hrs.

Then 3 * 1/8 means that she can does 3/8 of the job in that time.

 

If you work with that information, you will better understand the answer & if it is sstill unclear, please send me a message and I will try to help further.

 

 

Answer 2

C rate is 1job/8hr

 

D rate is 1 job/ 6 hr

 

hrs ( rate) = how much of job is finished.

 

3 hr (1/8) + 3 hr (1/6) = ?

 

3/8 + 3/6 + ?

 

3/8 + 1/2 = ?

 

3/8 + 4/8 = 7/8

 

1/8 of the job is left undone.