A certain business printer can print 40 characters per second, which

Rate at which business printer can print = 40 char per second
Rate at which an average printer can print = (40/4) char per second = 10 char per second

Average printer's rate = 5*Electric typewriter's rate
=>Electric typewriter's rate = 10/5 = 2 char per second = 2*60 char per min = 120 char per min

Answer D
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Hi All,

This question requires a bit of basic arithmetic AND that you pay attention to the units involved. 'Unit conversion' is something that you WILL be asked to do on a handful of Quant questions on Test Day, so it's important that you pay attention to the details that you are given (and the question that is ASKED).

To start, we know that a business printer can print 40 characters per second...which is 4 times faster than an average printer...

Average printer = 40/4 = 10 characters per second...this is 5 times faster than an electric typewriter...

Electric typewriter = 10/5 = 2 characters per second.

We're asked how many characters an electric typewriter can print in 1 MINUTE...

(2 characters per second)(60 seconds) = 120 characters per minute.

Final Answer:

GMAT assassins aren't born, they're made,
Rich

Rate at which business printer prints = 40 characters /second
Rate at which average printer prints = 10 characters /second
Rate at which electric typewriter prints = 2 characters /second which equates to 2*60 = 120 characters /minute
correct answer - D

Shortcut
Find the first rate in minutes.

"Certain" business printer's rate in characters, \(c\), per 1 minute:

\(\frac{40c}{1sec}*\frac{60}{60}=\frac{2,400c}{60secs}=\frac{2,400c}{1 minute}\)

Shortcut:
All rates are per 1 minute
Let the different machines be B, AP, and ET
Rate of B is 5 times as fast as that of AP
Rate of AP is 4 times as fast as that of ET

Hence B's rate is (5*4) = 20 times as fast as ET's rate

\(2,400c=20*ET\)
\(ET=\frac{2,400c}{20}=120c\)
\(ET=\frac{120c}{1 min}\)

In one minute, the electric typewriter can type 120 characters

Answer D

In steps
"Certain" business printer's rate from above:

\(\frac{2,400c}{1 minute}\)

That rate is 4 times as fast as the average printer's rate, AP:

\(2,400c=(4*AP)\)
\(AP=\frac{2,400c}{4}=600c\)
\(AP=\frac{600c}{1 min}\)

THAT per minute rate, AP, is 5 times as fast as an electric typewriter's per minute rate, ET:

\(600c=5*ET\)
\(ET=\frac{600c}{5}=120c\)
Electric typewriter rate: \(\frac{120c}{1min}\)

In one minute, the electric typewriter can type 120 characters

Answer D

*All rates based on a prior PER MINUTE rate are also per minute
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Since the rate of a business printer is 40 characters per second, then the rate of an average printer is 10 characters per second, and the rate of an electric typewriter is 2 characters per second. Therefore, in one minute, the electric typewriter can print 2 x 60 = 120 characters.

Answer: D
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Business printer: 40 characters per second

Average printer: \(\frac{40}{4}\) =10 characters per second [business printer is 4 times as fast as an average printer]

Electric typewriter: \(\frac{10}{5}\) = 2 characters per second [average printer can print 5 times as fast as an electric typewriter]

Characters per minute can an electric typewriter print: 1 sec = 2 characters => 1 * 60 = 60 * 2 = 120 [1 minute has 60 seconds]

Answer D

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