Rates-GMat Prep 2

medea66 wrote:I got lost after adding (1/9) and (1/7) to get (63/16).........

A's rate - 9000/hr
B's rate - 7000/hr

In 8 hrs.

A can produce - 72000 pencils
B can produce - 56000 pencils

Total needed =100000 pencils

B should be working for least amount of time.

100000-72000 = 28000

28000/7000 = 4 hrs.

4 hrs is least amount of time B has to spend.

Hence A is the answer.

Hope this help

A's rate : 9000
B's rate : 7000
Total to be produced : 100,000

To simplify things, we can take :
A's rate : 9
B's rate : 7
Total to be produced : 100
Max number of hours a machine can work : 8

How many hours minimum machine B needs to work to produce 100 pencils
Formula comes to :

9*8 + 7*x = 100
72 + 7*x = 100
7*x = 28
x = 4