Percentages
Percentages · ratio · proportion · partnership
12 min read · Updated 2026-05-25
What is a percentage?
A percentage is a fraction with 100 as its denominator, while ratio and proportion apply the same comparison to sharing quantities. CSAT rewards ten memorised fraction equivalents such as 1/8 = 12.5% and 1/3 = 33.33%, the successive-change rule x + y + xy/100, compound growth of (1 + r/100)^N, and partnership shares split as capital × time.
The story
It is CSAT 2024. Question 9:
"A merchant marks his goods up by 50% and gives a discount of 20% on the marked price. What is his profit/loss percentage?"
Two candidates. Candidate A sets up: Cost = 100, Marked Price = 150, Discount = 30, Selling Price = 120. Profit = 20%. 45 seconds.
Candidate B memorised "successive percentage formula": +50% then -20% → net = 50 - 20 - (50×20/100) = 50-20-10 = +20%. 8 seconds.
That 37-second saving — repeated across 12-15 percentage questions — is the difference between qualifying CSAT and not.
Percentages are the single most heavily tested topic in CSAT. Master 4 patterns + 3 formulas and you cover ~25% of the paper.
Why this matters for UPSC
For CSAT (Prelims Paper II, qualifying 33%):
- 15-20 questions out of 80 in every CSAT paper use percentages directly or indirectly. Profit/loss, discount, interest, growth, share price, election margin, exam %, salary hike — all percentage-based.
- Ratio + proportion = the language of comparison. Used in partnership (profit-sharing), mixtures, time-work, and DI graphs.
- Indian economy: GDP growth, inflation, tax slabs, share ratios — all percentages. Strong percentage intuition helps with GS-III too.
The ROI is unbeatable: 4 hours of focused practice + 60 questions = ~15-20% of CSAT marks locked in.