Percentage, Ratio and Average Shortcuts for MCQ Tests (With Worked Examples)

Basic Mathematics questions in General Ability tests are designed to be solved in under a minute, provided you know the right method. Most candidates lose time not because the maths is hard, but because they set up the calculation the long way.

Here are the methods that save the most time, each with a worked example.

1. Percentages as fractions

Many percentages are simple fractions in disguise. Knowing these turns multiplication into division:

Percentage	Fraction
50%	1/2
25%	1/4
20%	1/5
12.5%	1/8
10%	1/10
33⅓%	1/3

Example: What is 25% of 480? → 480 ÷ 4 = 120.

2. Percentage increase and decrease

Use a multiplier instead of working out the change separately:

• Increase by 15% → multiply by 1.15
• Decrease by 20% → multiply by 0.80

Example: A salary of Rs. 1,200 rises by 15%. → 1,200 × 1.15 = Rs. 1,380.

3. Successive changes are not added

A rise of 20% followed by a fall of 20% is not zero change.

Example: Take 100. After +20%: 120. After −20%: 120 × 0.8 = 96. The net result is a 4% decrease.

This exact question appears often because the “obvious” answer is wrong.

4. Profit and loss: always on the cost price

• Profit % = (Profit ÷ Cost price) × 100
• Selling price with profit p% = Cost price × (1 + p/100)

Example: A fan bought for Rs. 800 is sold at 20% profit. → 800 × 1.2 = Rs. 960.

Reverse example: Selling a chair for Rs. 1,150 gives a 15% profit. What was the cost? → 1,150 ÷ 1.15 = Rs. 1,000.

5. Dividing in a ratio

Add the parts, then take the share.

Example: Divide Rs. 1,600 between two people in the ratio 3 : 5. → Total parts = 8. First share = 1,600 × 3/8 = Rs. 600. Second share = Rs. 1,000.

6. Ratio with a known difference

Example: Two numbers are in the ratio 5 : 7 and differ by 18. → The difference in parts is 2, so 1 part = 9. The larger number is 7 × 9 = 63.

7. Averages: work with totals

Most average questions become easy once you convert averages back into totals.

Example: The average of 5 numbers is 40. Adding a sixth number makes the average 42. What is the sixth number? → Old total = 5 × 40 = 200. New total = 6 × 42 = 252. Sixth number = 252 − 200 = 52.

8. Average speed is not the simple average

For a round trip at two different speeds over the same distance:

Average speed = 2 × a × b ÷ (a + b)

Example: 40 km/h one way and 60 km/h back → 2 × 40 × 60 ÷ 100 = 48 km/h, not 50.

9. Simple interest in one line

SI = P × R × T ÷ 100

Example: Rs. 5,000 at 8% for 3 years → 5,000 × 8 × 3 ÷ 100 = Rs. 1,200.

How to make these automatic

Knowing a method is not the same as being fast with it. Pick one method a day and solve ten questions using only that method. After two weeks, all nine will feel natural.

Then practise mixed questions under time pressure with our Percentages, Profit and Loss and Ratio, Average and Ages sets. Every answer includes a step-by-step solution.