Free CAT Questions

You get official solutions with each question, and our insights to help you track your preparation.

Click here!

MBA Prep articles

  • Discussion in CAT
  • Created by @Apurv
  • 08:43 PM, 15 Aug '14


View more posts in MBA Prep articles
guest_writer
Guest @guest_writer 18.0 k
[image] _(Photo credit: Jimmie)_ Data Interpretation questions typically have large amounts of data given in the form of tables, pie-charts, line graphs or some non-conventional data representation format. The questions are calculation heavy and typically test your approximation abilit...

Tricks to speed up calculations for Data Interpretation questions in CAT 2011




(Photo credit: Jimmie)


Data Interpretation questions typically have large amounts of data given in the form of tables, pie-charts, line graphs or some non-conventional data representation format. The questions are calculation heavy and typically test your approximation abilities. A very large number of these questions check your ability to compare or calculate fractions and percentages. If you sit down to actually calculate the answer, you would end up spending more time than required. Here are few ideas that you can use for approximation.



Funda 1 Calculating (Approximating) Fractions


When trying to calculate (approximate) a fraction p/q, add a value to the denominator and a corresponding value to the numerator before calculating (approximating).



Example,


What is the value of 1789/762 ?


First the denominator. We can either take it close to 750 or to 800. Lets see how it works in both cases. We know that the answer is between 2 and 3, so for adding values / subtracting values from the denominator or the numerator, I will consider a factor of 2.5.


Case 1: 762 is 12 above 750, so I will subtract 12 from the denominator. Keeping the factor of 2.5 in mind, I will subtract 25 from the numerator.


My new fraction is,


(1789 - 25) / (762 - 12) = 1763 / 750 = 1763 ? (4 / 3000 ) = 7.052 / 3 = 2.350666


Actual answer is 2.34776.


As you can see, with very little effort involved in approximation, we arrived really close to the actual answer.


Case 2: 762 is 38 below 800, so I will add 38 to the denominator. Keeping the factor of 2.5 in mind, I will add 95 to the numerator.


My new fraction is,


(1789 + 95) / (762 + 3 = 1884 / 800 = 2.355


As you can see, even this is close to the actual answer. The previous one was closer because the magnitude of approximation done in the previous case was lesser.



Funda 2 Comparing Fractions


If you add the same number to the numerator and denominator of a proper fraction, the value of the proper fraction increases.


If you add the same number to the numerator and denominator of an improper fraction, the value of the improper fraction decreases.


Note: You can remember this by keeping in mind that,


1/2 < 2/3 < 3/4 < 4/5 ...


and


3/2 > 4/3 > 5/4 > 6/5 ...



Example,


Arrange the following in increasing order: 117/229, 128/239, 223/449.


Lets first compare 117/229 & 128/239.


If we added 11 to the numerator and the denominator of the first proper fraction, the resulting proper fraction would be 128/240, which will be bigger in value than the original (as per Funda 2).


We know that 128/240 is smaller than 128/239, as the latter has a lower base.


So, 117/229 < 128/240 < 128/239


? 117/229 < 128/239



Now lets compare 117/229 and 223/449.


If we added 11 to the numerator and the denominator of the second proper fraction, the resulting proper fraction would be 234/460, which will be bigger in value than the original.


If we doubled the numerator and denominator of the first proper fraction, the resulting proper fraction would be 234/458.


We know that 234/460 is smaller than 234/458, as the latter has a lower base.


So, 223/449 < 234/460< 234/458


? 223/449 < 117/229


Using the above two results, we can say that 223/449 < 117/229 < 128/239


Note: This question can be solved much simply by just looking at the numbers and approximately comparing them with 12. I used this long explanation to illustrate the funda given above.



Following are a few other shortcuts that might come in handy during DI-related calculations.



Funda 3 Percentage Growth


If the percentage growth rate is r for a period of t years, the overall growth rate is approximately: rt + t * (t-1) * r2 / 2


Note: Derived from the Binomial theorem, this approximation technique works best when the value of 'r' is small. If the rate is above 10%, then this approximation technique yields bad results. Also, if the rate is 5% then r = 0.05; if the rate is 7.2% then r = 0.072.



Funda 4 Comparing Powers


Given two natural numbers a and b such that a > b > 1,


ab will always be less than ba


Note: There are only two exceptions to this funda. I hope someone in the comments will point them out (anyone?).



Author Ravi Handa has taught Quantitative Aptitude at IMS for 4 years. An alumnus of IIT Kharagpur where he studied a dual-degree in computer science, he has also written a book on business awareness.




  • 174 Likes   80Comments
  • in funda 1: sir, how you determined factor ans. lies be.... 13 Jun.
  • can any one tel me wat is factor 2.5. 17 Jun.
  80 Comments
anku123
akshay ghosh @anku123 61
@ravihanda :In funda 1 What is the logic behind 2.5 do we need to take it for every case of division or what do throw some light and clear the doubt...

essay.kay
Saurabh Kulkarni @essay.kay 74
@anku123 : Consider a fraction x/y. Let its value be 3. Now if I add 3 to the numerator and 1 to the denominator, its value will be:
(x+3)/(y+1) = (3y+3)/(y+1) = 3
This means that if you add a value 'a' to the numerator and a value 'b' to the denominator, and a/b=x/y, the value will remain x/y
In Sir's eg., we can deduce that the value of the fraction is between 2 and 3, but we don't know the exact value (if we did, we wouldn't need an approximation technique ). So, he assumes that the value is 2.5. So he subtracted 12 from the denominator to reach a round figure (750). And 30 (12*2.5) is subtracted from the numerator (I dunno why he subtracted 25). After this, the calculation becomes simple.
essay.kay
Saurabh Kulkarni @essay.kay 74
@ravihanda : Sir, can you give some calculation techniques for approximation of larger fractions? Like say, 5287/234...
Psuwin
A G @Psuwin 161
i think the best in case of large fractions is to break it in parts... like get 4680 out of 5287....607 left which is between 2 and 2.5.... it can be seen easily... 234 * 3=702... diffrnce between 702 and 607 is 95... which amounts to less than half ... or 23.4 *4 is approx 95... so it has to be 0.4 less than 1 so the ans comes out to be... around 22.6
lovedeep
lovedeep kumar @lovedeep
In (Funda 1 Calculating (Approximating) Fractions), how we subtract or add from numerator .
lovedeep
lovedeep kumar @lovedeep
I mean how we subtract 25 in case 1 and add 95 in case 2 to the numerator. From where 25 and 95 comes ???
89amit
amit gupta @89amit

in funda 1:  sir, how  you determined factor ans. lies between 2 and 3 only.