If two printing machines work simultaneously at their respective

Question

If two printing machines work simultaneously at their respective constant rates, how much time (in minutes) will it take for them to print out 100 copies of a photograph?

(1) One of the machines prints at thrice the constant rate of the other machine.
(2) One of the machines prints at a constant rate of 15 prints per minute.

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suntprovident · Answer

The question asks us to share the time that two machines assumed (A and B) working together can print 100 copies ?

1. Statement A gives us the ratios of the rate of two machines i.e. 3:1 but not the actual time hence clearly insufficient. Also eliminate D
2. Statement B gives us that one machine can print in 15 mins. We don't know anything about another maching. Eliminate D

3. Combining - we know one machine can do it in 15 mins and ratio is 3:1 but whether this is the faster or slower machine is not known. The answer could be 15 & 45 mins or 15 & 5 mins. Hence insufficient.

dhart · Answer

Stmt 1 + smt 2 gives rate of a machine 15 prints and another machine b as thrice of a henece suffc.

option c

SportEarth · Answer

It is not mentioned anywhere that 15 prints are done by a machine of the lowest efficiency. There are two possible combinations: (5,15) or (15,45) if we take statements 1 and 2 together.

dhart · Answer

yes, stmt 1 and stmt 2 give one of them as 15 prints , and one as thrice of the other ,whats what , no one knows

insuff e

ThickRiver · Answer

E is right, and I think it's worth spelling out exactly why, because this is one of those DS questions where the ambiguity is the entire point.

1. Statement 1 tells you one machine prints at three times the rate of the other. That's a ratio, no actual speed. Not sufficient on its own.

2. Statement 2 tells you one machine prints at 15 per minute. A number without an identity, still not sufficient alone since you don't know if this is the fast one or the slow one.

3. Combine them, and here's the trap. You know one machine's absolute rate is 15 and the other is three times some rate, but the statements never tell you which machine is which. If the 15-per-minute machine is the slower one, the faster one prints at 45, combined rate is 60 per minute, and 100 copies takes 5/3 minutes. If the 15-per-minute machine is the faster one, the slower one prints at 5, combined rate is 20 per minute, and 100 copies takes 5 minutes. Two different times, same two statements. That's E.

The takeaway that helped me stop falling for this pattern: whenever a DS statement gives you a ratio between two unnamed things, and another statement gives you one absolute value without saying which thing it belongs to, assume there's an assignment trap until you've proven otherwise.

If two printing machines work simultaneously at their respective

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GMAT Data Sufficiency (DS) Questions

­If two printing machines work simultaneously at their respective

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615 to 715 in 15 Days (Ria's Strategies)

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If two printing machines work simultaneously at their respective