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TNPSC ratio and proportion practice questions with worked answers

By the PrepMatic team · Updated 9 Oct 2026 · 4 min read

Ratio and proportion is one of the cleanest topics in the aptitude part of the TNPSC paper. The ideas are small, the questions are short, and the method hardly changes: turn the ratio into parts, find what one part is worth, and rebuild the answer. The notification lists it among the ten aptitude topics, with the Group 4 Part C aptitude section carrying 15 of the 200 questions. The five questions below show the usual types. The full guide to this subject is TNPSC aptitude and mental ability.

What this topic covers

• Ratio: simplifying, comparing and combining ratios.
• Proportion: direct and inverse proportion, and the special proportionals.
• Sharing in a ratio: money, ages and quantities.
• Mixtures: two quantities in a stated ratio.

Sample questions

Question 1

₹1,200 is divided between A and B in the ratio 3 : 5. A's share is:

• A. ₹750
• B. ₹600
• C. ₹450
• D. ₹400

Question 2

If a : b = 2 : 3 and b : c = 4 : 5, then a : c is:

• A. 8 : 15
• B. 2 : 5
• C. 4 : 5
• D. 6 : 7

Question 3

The fourth proportional to 4, 6 and 8 is:

• A. 10
• B. 12
• C. 16
• D. 24

Question 4

The ages of a father and his son are in the ratio 7 : 2. The father is 35 years old. The son's age after 5 years will be:

• A. 10 years
• B. 12 years
• C. 15 years
• D. 20 years

Question 5

A mixture of 18 litres contains milk and water in the ratio 5 : 1. The quantity of water is:

• A. 15 litres
• B. 5 litres
• C. 2 litres
• D. 3 litres

Answers and explanations

1. C. The total number of parts is 3 + 5 = 8, so one part is 1,200 ÷ 8 = ₹150. A gets 3 parts: 3 × 150 = ₹450. B gets ₹750.
2. A. Make the middle term the same. b is 3 in the first ratio and 4 in the second, so use 12. Then a : b = 8 : 12 and b : c = 12 : 15, which gives a : c = 8 : 15.
3. B. If 4 : 6 = 8 : x, then x = 6 × 8 ÷ 4 = 12.
4. C. One part is 35 ÷ 7 = 5, so the son is 2 × 5 = 10 years old now. After 5 years he will be 15. Answering 10 is the usual slip: the question asks about 5 years later.
5. D. The mixture has 5 + 1 = 6 parts, and each part is 18 ÷ 6 = 3 litres. Water is 1 part, so 3 litres, and milk is 15 litres.

How to prepare ratio and proportion

Adopt the "parts" method for every question in this chapter. Write the ratio, add the parts, divide the total by that sum, and multiply back. It works for money, ages, mixtures and angles, and it removes the need to remember separate formulas.

Next, practise two skills that appear in harder questions. The first is equalising a common term, as in question 2, which is also the key step in chained ratios. The second is the ages trick: when a ratio of ages is given for now, the difference between the ages stays fixed. If the father is 35 and the son 10, the gap is 25 in any year.

Keep your arithmetic sharp by checking that the parts add up to the total. For example, in question 1 you can confirm 450 + 750 = 1,200. It takes three seconds and catches slips.

Ratio connects directly to TNPSC percentage practice, since a percentage is a ratio out of 100, and to TNPSC time and work practice, where days and rates are inversely proportional.

Take the full topic test on PrepMatic

A PrepMatic topic test (about 15 questions, 30 minutes) will tell you whether your ratio work is fast enough for exam conditions. If you are studying beside a job, choose a light pace in the study plan and use the topic test as a short weekday session. The free Basic plan includes 5 topic tests and 2 mock tests a month.

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