# Basics of Data Interpretation – Approximation

Monday, March 1st, 2021 Data Interpretation questions typically have large amount of data given in the form of tables, pie charts, line graphs or some non-conventional 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 and most of us can’t afford to lose precious time during competitive exams like CAT, XAT, IIFT etc.  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

Now for the denominator, either we take it close to 750 or to 800. Let’s see how it happens in both cases. Clearly 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 30 from the numerator.

My new fraction is :

(1789-30)/(762-12) = 1759/750 = (1759*4)/3000 = 7.036/3 = 2.34533333

Actual answer is 2.34776.

As you can see, with very little effort involved in approximation, we got 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+38)
1884/800
2.355

As you can see, even this is close to the answer.

## 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 a proper 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

Let’s first compare 117/229  & 128/239.

If we add 11 to the numerator and the denominator of the first proper fraction, the resulting proper fraction would be 128/240, which will be bigger than the original.

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 let’s compare 117/229 and 223/449.

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

If we double 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 1/2. I used this long explanation to illustrate the funda given above.

#Given below are few other shortcuts that might come in handy in 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)*r^2/2

Note: Derived from the Binomial theorem, this approximation technique works best, when the value of r is small. If the rate goes above 10%, then this approximation technique gives 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 that natural numbers 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.

As I end this post, I am also wondering if “Approximation of Dreams… Oops! Data” would have been a better title.

## Other posts related to Logical Reasoning and Data Interpretation

### CAT Questions related to Logical Reasoning and Data Interpretation

All questions from CAT Exam Logical Reasoning and Data Interpretation
Logical Reasoning – Set 1: A high security research lab requires the researchers to set a pass key sequence based on the scan of the five fingers of their left hands.
Logical Reasoning – Set 2: Eight friends: Ajit, Byomkesh, Gargi, Jayanta, Kikira, Manik, Prodosh and Tapesh are going to Delhi from Kolkata
Logical Reasoning – Set 3: In an 8 X 8 chessboard a queen placed anywhere can attack another piece if the piece is present in the same row
Logical Reasoning – Set 4: A tea taster was assigned to rate teas from six different locations – Munnar, Wayanad, Ooty, Darjeeling, Assam and Himachal.
Logical Reasoning – Set 5: Four cars need to travel from Akala (A) to Bakala (B). Two routes are available, one via Mamur (M) and the other via Nanur (N).
Data Interpretation – Set 1: At a management school, the oldest 10 dorms, numbered 1 to 10, need to be repaired urgently
Data Interpretation – Set 2: An old woman had the following assets:(a) Rs. 70 lakh in bank deposits
Data Interpretation – Set 3: There were seven elective courses – El to E7 – running in a specific term in a college.
Data Interpretation – Set 4: Funky Pizzaria was required to supply pizzas to three different parties.
Data Interpretation – Set 5: Simple Happiness index (SHI) of a country is computed on the basis of three parameters: social support (S), freedom to life choices (F) and corruption perception (C).

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### One response to “Basics of Data Interpretation – Approximation”

1. zed says:

Exception for Funda 4:
a,b being 4,2 and 3,2

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