AAPL wrote: ↑Tue Jul 05, 2022 1:41 pm

**GMAT Prep**
Working at their respective constant rates, machine A and machine B can fill a certain order in 3 hours and 6 hours, respectively. If the two machines work simultaneously at their respective constant rates, how many hours does it take the two machines to fill 1/2 of that order?

A. 1/2

B. 3/4

C. 1

D. 1 1/4

E. 1 1/2

OA

C

One approach is to

assign a "nice value" to the job.

That is, a value that works well with the given information of 3 hours and 6 hours

So let's say the order consists of making

18 widgets

*Working alone at their respective constant rates, machine A and machine B can fill a certain order in 3 hours and 6 hours, respectively*
In other words, Machine A can make

18 widgets in 3 hours, which means Machine A's RATE =

6 widgets per hour

This also tells us that Machine B can make

18 widgets in 6 hours, which means Machine B's RATE =

3 widgets per hour

*If the two machines work simultaneously at their respective constant rates, how many hours does it take the two machines to fill 1/2 of that order?*
COMBINED rate =

6 +

3 =

**9** widgets per hour

We want to fill 1/2 the order.

1/2 of

18 widgets is

**9** widgets

So we want to make

**9** widgets

**time = output/rate**
So, time =

**9**/

**9** = 1 hour

Answer: C

Cheers,

Brent