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kginena
Students
 
Posts: 7
Joined: Mon May 14, 2012 2:31 am
 

arithmetic mean comparison question CAT 5

by kginena Sat Jun 16, 2012 9:43 am

Question:

x > y

Quantity A

The average (arithmetic mean) of x, x, x, y, and y

Quantity B

The average (arithmetic mean) of x, x, and y

Quantity A is greater.
Quantity B is greater.
The two quantities are equal.
The relationship cannot be determined from the information given.

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Rather than solving this question algebraically (which is what the solution does) i just used sample figures. I used x=10 and y=5 and got the correct answer. So, is my method of solving the question correct or is it just a fluke that I got the correct answer?
esledge
 
Posts: 23
Joined: Wed Apr 06, 2011 7:09 am
 

Re: arithmetic mean comparison question CAT 5

by esledge Sun Jun 24, 2012 2:04 pm

Hi kginena,

In general, you should test numbers with the intent of Proving D. That is, if you can test two sets of numbers and get different results (e.g. Quantity A is greater in one case, but the quantities are equal in the other), then you have proven the answer is D. But if you plug in several cases and always find that Quantity B is greater, while you have reason to believe the answer could be (B), you haven't proven that it definitely is.

So, it is a bit of a fluke that testing one set of numbers led you to the right answer here. In fact, if the x > y constraint were removed from this question, your test case would show that Quantity B is greater, but a second case (say, x = 1 and y = 10) could show that Quantity A is greater. If not for that constraint, your plugging approach would have yielded the wrong answer.

In short, by plugging numbers, you might notice a pattern that Quantity B is greater, but you should always plug more than one set of test numbers. And it is often only with algebra that you can prove why the pattern exists.