Bunuel wrote:
Printing press X can print an edition of a newspaper in 12 hours, whereas press Y can print the same edition in 18 hours. What is the total number of hours that it will take the two presses, working together but independently of one another, to print the same edition?
A. 15
B. 7.4
C. 7.2
D. 7.0
E. 6.8
PS20370
Let's
assign a "nice value" to the job a printing an edition of a newspaper.
We're looking for a number that works well with the given information: 12 hours and 18 hours
Since
36 is the least common multiple of 12 and 18, let's say the job requires the printing presses to print a total of
36 newspapers
Printing press X can print an edition of a newspaper in 12 hoursIn other words, printing press X can print
36 newspapers in 12 hours
So, its RATE =
3 newspapers per HOUR
Printing press Y can print an edition of a newspaper in 18 hoursIn other words, printing press Y can print
36 newspapers in 18 hours
So, its RATE =
2 newspapers per HOUR
What is the total number of hours that it will take the two presses, working together but independently of one another, to print the same edition?The combined RATE of the two printing presses =
3 +
2 =
5 newspapers per HOUR
Time = output/rateSo the time to print 36 newspapers =
36/
5 =
7.2Answer: C
Cheers,
Brent
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Brent Hanneson – Creator of gmatprepnow.com
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