BTGModeratorVI wrote: ↑Wed Oct 07, 2020 7:16 am
Working alone, R can complete a certain kind of job in 9 hours. R and S, working together at their respective rates, can complete one of these jobs in 6 hours. In how many hours can S, working alone, complete one of these jobs?
(A) 18
(B) 12
(C) 9
(D) 6
(E) 3
Answer:
A
Source: official guide
One approach is to assign a "nice" value to the entire job.
So let's use a number that works well with the two given values of 9 hours and 6 hours.
Let's say the job consists of making
54 widgets.
Working alone, R can complete a certain kind of job in 9 hours.
In other words, R can make
54 widgets in 9 hours.
This means R's RATE = 6 widgets per hour
R and S, working together at their respective rates, can complete one of these jobs in 6 hours
In other words, R and S can make
54 widgets in 6 hours.
This means their COMBINED rate = 9 widgets per hour
9 - 6 = 3
So, S's RATE =
3 widgets per hour
In how many hours can S, working alone, complete one of these jobs?
Another words, how much time will it take S to make
54 widgets?
Time = output/rate
So, time =
54/
3 = 18 hours
Answer: A
Cheers,
Brent
