alex.gellatly wrote:Working alone at its own constant rate, a machine seals k cartons in 8 hours, and working alone at its own constant rate, a second machine seals k cartons in 4 hours. If the two machines, each working at its own constant rate and for the same period of time, together sealed a certain number of cartons, what percent of the cartons were sealed by the machine working at the faster rate?
(A) 25%
(B) 33 1/3%
(C) 50%
(D) 66 2/3%
(E) 75%
Thanks
We can also solve this question by plugging in a convenient value for k.
Let's say that
k=8.
So, the slower machine seals
8 cartons in 8 hours, which means it seals
1 carton per hour.
This also means that the faster machine seals
8 cartons in 2 hours, which means it seals
2 carton per hour.
Now the question considers a scenario in which the 2 machines, working together, and for the
same period of time, sealed a certain number of cartons.
Well, let's say they worked for one hour.
This means they sealed a total of
3 cartons, and the faster machine sealed
2 of those cartons.
So, the faster machine sealed 2/3 (66 2/3%) of the cartons.
So, the answer is
D
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
