BTGModeratorVI wrote: ↑Wed Jul 29, 2020 2:47 pm
Working alone 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
Answer:
C
Source: GMAT prep
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
Brent Hanneson - Creator of GMATPrepNow.com
