Quantitative Aptitude:Useful ratios and percentages to speed up problem solving and analysis

Useful ratios and percentages to speed up problem solving and analysis

Many questions in numerical reasoning, data interpretation and other problem solving tests involves the usage of percentages and ratios. You may need to multiply by percentages, use ratios as part of calculations, divide by decimals and so on. Often, these % and ratios tend to be "familiar" (it's rare for questions to ask you to calculate 39.2% of something - it will probably be 40%)

Below is a table of popular ratios with their equivalent percentages and decimals. Knowing them at the top of the mind can significantly speed up mental or calculator based calculations by helping you 'skip' intermediate steps.

Let's look at some examples -

What is 75% of 250? Would you do 75% x 240? No. What you should do is (3/4) x 240 = 3 x 60 = 180. Which is much simpler than doing 240 x 0.75. Similarly, why do x 15% when you can do x 3/20?

Look for opportunities to use simple fractions instead of 2 digit multiplications.

Whether you are strong with math or not, learn these ratios well and they can help you speeding up approximations and a lot of other calculations.

Fraction	%	Decimal
1/3	33%	0.33
1/4	25%	0.25
1/5	20%	0.20
1/6	17%	0.17
1/7	14%	0.14
1/8	13%	0.13
1/9	11%	0.11
1/10	10%	0.10
1/11	9%	0.09
1/12	8%	0.08
1/20	5%	0.05
1/40	2.5%	0.025
2/5	40%	0.40
3/5	60%	0.60
3/8	38%	0.38
3/4	75%	0.75
3/20	15%	0.15
4/5	80%	0.80
5/9	56%	0.56

A few examples:

- What is 75% of 120? (120 x 3/4 = 90!)
- 3/5th of a company's sales came from book subscriptions (..you mean 60%!)
- Expenditure is 0.38 of the sales (= sales x 3/8)

and so on. Success in numerical reasoning tests is not just about knowing how to solve a problem, it's also about how to solve a problem quickly, efficiently and by intelligent application of mathematical shortcuts and eliminations. Knowing how to shave a few seconds off of each question will simply mean solving a couple of extra questions which might mean a big difference in the final outcome.