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Engine A can work 5 hours on 10 liters of fuel

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Engine A can work 5 hours on 10 liters of fuel

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Engine A can work 5 hours on 10 liters of fuel while engine B can work 3 hours on 15 liters of fuel. If engine efficiency is defined as a reciprocal to the hourly fuel consumption rate, what is the ratio of the efficiency of engine B to that of engine A?

A)2/5
B)1/2
C)2
D)5/2
E)3

OA: A

What is hourly fuel consumption rate ?

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NandishSS wrote:
Engine A can work 5 hours on 10 liters of fuel while engine B can work 3 hours on 15 liters of fuel. If engine efficiency is defined as a reciprocal to the hourly fuel consumption rate, what is the ratio of the efficiency of engine B to that of engine A?

A)2/5
B)1/2
C)2
D)5/2
E)3

OA: A

What is hourly fuel consumption rate ?
You can think of any rate as "task/time period." So here the fuel consumption rate for A is 10 liters/5 hours = 2 liters/hour and the consumption rate for B is 15 liters/3hours = 5 liters per hours.

If the engine efficiency is the reciprocal of this figure, then the engine efficiency for A is 1/2 and for B it's 1/5.

We want the ratio of the efficiency of B to the efficiency of A, or (1/5)/(1/2) = 1/5 * 2/1 = 2/5. The answer is A

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Note, also, that it's often the case that a question will have both the correct answer and a trap answer among the answer choices. In this case, because we're dealing with reciprocals, it stands to reason that there's a good chance 2/5 and 5/2 represent a correct answer and a trap. (Of course, there are exceptions.) If you're able to see that B's engine efficiency is less than that of A's, you can jump right to the answer almost immediately.

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NandishSS wrote:
Engine A can work 5 hours on 10 liters of fuel while engine B can work 3 hours on 15 liters of fuel. If engine efficiency is defined as a reciprocal to the hourly fuel consumption rate, what is the ratio of the efficiency of engine B to that of engine A?

A)2/5
B)1/2
C)2
D)5/2
E)3

OA: A

What is hourly fuel consumption rate ?
"Hourly fuel consumption rate" means the amount of fuel consumed in an hour measured in Liter per hour

Thus, efficiency = Reciprocal of (Liter per hour) = Hour per liter

Hope this helps!

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-Jay
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