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Ballparking in GRE Math-Arithmetic

gre-12Sometimes you might just get stuck on a question and not know how to proceed. It may also happen that you know how to solve the question but have very little time to complete. At such times, Ballparking may just help you to get your answer right on the GRE. Ballparking is a strategy which involves eliminating wrong answer choices and estimating the possibly right answer by doing some approximate calculations.

Let’s understand this better with an example.
1. If P=91/2 -91/3-91/5, Then P is

  • A. less than 0
  • B. Between 0 and 1
  • C. Between 1 and 2
  • D. Between 2 and 3
  • E. Greater than 3

images-136x150A normal way of solving this question would be to use the calculator, but it is not possible on the GRE. As the onscreen calculator will not help you to find the cube root or the fifth root!

 

Now square root of 9 is 3 and if you have to subtract 91/3 and 91/5 from 3 then P’s got to be less than 3!  So answer choice E gets eliminated.

Now since 81/3 is 2, we can say that 91/3> 2. So 3 – (some no >2) means P must be less than 1. Eliminate C and D.

Since 11/5 = 1, we can say that 91/5>1.

That means P = 3 – (some no. >2) – (some no. >1) and this makes P negative. The answer is A

Ballparking works very well when the answer choices are far apart as in the example below:

2. Which of the following is nearest to

I3

 

  • A. 15
  • B. 10
  • C. 7
  • D. 3
  • E. 1

The numbers look quite horrible but let’s just replace the decimals with whole numbers and compute. First let’s round off the decimal numbers and then do some approximation.

A-1

 

Capture-1

Wait a moment! E is not the answer!
Be careful! The question has a 3 in the beginning and hence the answer is D!
You will see more of Ballparking in our next blog: Ballparking in GRE Math-Geometry

 

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