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Published on November 29th, 2010 In category Education | Maths

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Using Approximation to save time for solving maths problems

Solving Problem by ApproximationsQuantitative aptitude is most time consuming part in most of the competitive exams be in CAT, GMAT or any other civil services entrance examinations. The trick in such examinations to identify the correct questions to solve in fastest possible manner and approximate the best answers from the available choice. As long as you are able to identify the correct choice from multiple answers available, it really doesn’t matters how the answer was decided. For example  Take a look at this problem

81.25  x  52.06

The problem looks complicated and if you will use calculator, I guess it will take ages to reach the answer. Howerver, If you use the power of the approximation. This problem can be solved quite quickly. 81.25 can be approximated as 80 and 52.06 as 50

80  x  50

Now this problem can be solved very easily and answer can be approximated to nearest choice.

Now lets take a question that has been earlier asked in many competitive exams like CAT, GMAT and Bank probationary exams.

Questions: Which power to the 10 is nearest to the result of the product of all prime numbers less than 20.  The choice available are as follows :   a) 10^3 b) 10 ^ 7 c) 10^5 d) 10^6

Solution is as follows:  Collect all the prime numbers less than 20. They are 2,3,5,7,11,13,17,19. If I need to multiply in sequence it will be tough, instead I will use group and approximate maths trick

( 2 x5) = 10

( 3 x 7) = 21 approximate as 20

(11 x 19 ) = 209 approximate to 200

(13 x 19 ) = 221 approximate to 200

Now if we multiple 10 x 20x 200 x 200 and calculate the answer it is as follows as we can easily approximate 8 x 10^6 . So the answer can be easily approximated very nearly to 10^7

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