Why this topic matters · 8 min read
Ratio, Proportion and Percentage form a high-frequency cluster in CTET Paper II Math-Science section. Expect 3-5 direct questions per paper testing both content knowledge (solving problems) and pedagogical knowledge (how to teach these concepts to Class 6-8 students, common misconceptions children have, and appropriate teaching strategies). Questions often blend a numerical problem with a pedagogy angle, so knowing the concept AND how children learn it is essential.
Ratio — Core Concept
A ratio compares two quantities of the same kind using division. It tells us how many times one quantity is compared to another. Written as a:b or a/b, it has no units. Ratio is NOT a fraction in the usual sense — it is a relationship. Teachers must help students understand that 2:3 and 4:6 represent the same relationship (equivalent ratios), just like equivalent fractions.
- Ratio a:b means a divided by b. Both quantities must be in the same unit before comparing.
- Equivalent ratios: multiply or divide both terms by the same non-zero number.
- Ratio in simplest form: divide both terms by their HCF.
- Order matters: 3:5 is NOT the same as 5:3.
- A ratio has no units — always simplify and express as whole numbers.
- Dividing a quantity in a given ratio: if total is T and ratio is a:b, first part = (a/a+b) x T.
Key formulas
Dividing in ratio
Part1 = (a / (a+b)) x Total, Part2 = (b / (a+b)) x Total
When: When a quantity is to be split in ratio a:b
Simplest form
Simplest ratio = (a / HCF(a,b)) : (b / HCF(a,b))
When: To reduce a ratio to lowest terms
Worked examples
Divide Rs 720 in ratio 3:5. Total parts = 8. Part1 = (3/8) x 720 = Rs 270. Part2 = (5/8) x 720 = Rs 450. Check: 270 + 450 = 720. Correct.
Are 4:6 and 10:15 equivalent? 4/6 = 2/3. 10/15 = 2/3. Yes, they are equivalent ratios.
Proportion — Core Concept
Proportion is an equality of two ratios. If a:b = c:d, we say a, b, c, d are in proportion. This is written as a:b :: c:d and read as 'a is to b as c is to d'. The key rule is the Cross Product Property: product of extremes = product of means. CTET often tests whether students and teachers can distinguish between direct and inverse proportion — a critical Class 8 concept.
- Proportion: a:b :: c:d means a x d = b x c (extremes x extremes = means x means).
- Extremes are the outer terms (a and d); Means are the inner terms (b and c).
- Direct proportion: as one quantity increases, the other increases in the same ratio. y = kx.
- Inverse proportion: as one quantity increases, the other decreases. x x y = constant.
- Continued proportion: a:b :: b:c means b squared = a x c. Here b is called mean proportional.
- Fourth proportional: if a:b :: c:x, then x = (b x c) / a.
Key formulas
Cross product rule
a:b :: c:d => a x d = b x c
When: To verify or find a missing term in a proportion
Mean proportional
b = square root of (a x c)
When: When a, b, c are in continued proportion
Direct proportion
x1/y1 = x2/y2
When: When two quantities increase or decrease together
Inverse proportion
x1 x y1 = x2 x y2
When: When one increases and the other decreases proportionally
Worked examples
Find x: 3:4 :: 9:x. Cross multiply: 3 x x = 4 x 9 => x = 36/3 = 12.
5 workers finish a job in 12 days. How many days for 3 workers? Inverse proportion: 5 x 12 = 3 x d => d = 60/3 = 20 days.
Percentage — Core Concept
Percentage means 'per hundred'. It is a special ratio where the second term is always 100. Percentage is one of the most practically applicable concepts in Class 6-8 math and is used in profit-loss, discount, tax, and interest problems. CTET Paper II tests both numerical percentage problems and the pedagogical question of why students confuse percentage with fraction or ratio.
- Percentage = (Part / Whole) x 100. To convert fraction to %, multiply by 100.
- To find X% of a number N: (X/100) x N.
- Percentage increase = (Increase / Original) x 100.
- Percentage decrease = (Decrease / Original) x 100.
- If price increases by R%, new price = Original x (1 + R/100). Decreases: multiply by (1 - R/100).
- Percentage and fraction link: 25% = 1/4, 50% = 1/2, 75% = 3/4, 33.33% = 1/3, 66.67% = 2/3.
Key formulas
Basic percentage
Percentage = (Part / Whole) x 100
When: To express a part as percentage of whole
Percentage change
% change = ((New - Old) / Old) x 100
When: For increase or decrease problems
Finding the original
Original = (Given value / (100 +/- R)) x 100
When: When final value after % change is given and original is asked
Worked examples
A shirt costs Rs 800. It is sold at 15% discount. Discount = 15% of 800 = 120. Selling price = 800 - 120 = Rs 680.
Marks increased from 40 to 50. % increase = (10/40) x 100 = 25%.
Pedagogy Angle — How CTET Tests It
CTET Paper II does NOT just test whether you can solve ratio-proportion-percentage problems. It tests whether you understand how Class 6-8 children learn these topics. Expect questions about common student errors, best teaching approaches, and appropriate use of manipulatives or real-life contexts. The NCF and NCERT approach emphasizes using everyday situations like recipe scaling, map reading, and discount shopping to introduce these concepts.
- Common student misconception: treating ratio as subtraction comparison instead of division comparison (e.g., saying 5 and 3 differ by 2 instead of ratio 5:3).
- Children often confuse percentage decrease applied twice: 20% off then 20% on does NOT return to original price.
- Best teaching strategy: use concrete-to-abstract approach — start with actual objects, then diagrams, then symbols.
- Unitary method is the bridge concept linking ratio to proportion — teach it before formal proportion.
- Error-analysis questions: a teacher asks why a student wrote 2:3 = 3:2. The answer is that the student treats ratio like addition (commutative) — ratio is NOT commutative.
⚠ Common mistakes to avoid
- Confusing direct and inverse proportion — students (and aspirants) mark direct proportion formula for a speed-workers problem that is actually inverse proportion. Always ask: if one goes up, does the other go up (direct) or down (inverse)?
- In percentage change problems, using the WRONG base. Percentage increase uses original as base, not the new value. CTET often traps you by giving the new value and asking for original.
- Writing ratio without checking units — comparing 500g and 2kg as 500:2 instead of first converting to 500:2000 = 1:4.
- In proportion extremes-means rule, swapping which terms are extremes and which are means — remember Extremes are at the Edges (outer positions).
- Thinking 20% increase followed by 20% decrease returns to original. It does not — net effect is a 4% decrease. CTET has asked this pedagogy question multiple times.
🧠 Memory aids
- DEER for Proportion: Divide, Extremes Equal, Reverse for inverse. Cross multiply D x E = E x D reminds you extremes times extremes = means times means.
- Percent Fraction Cheat: 10%=1/10, 20%=1/5, 25%=1/4, 50%=1/2, 75%=3/4, 33%=1/3. Memorize these 6 and you save 30 seconds per question.
- DIPS for proportion types: Direct means In Proportion Same direction, Inverse means Product is Same (x1 y1 = x2 y2).
- Ratio Rule reminder: Same Units, Same Order. Before writing a ratio, make units same. Order changes meaning — salary of A to B is NOT same as B to A.
🎯 CTET PAPER II exam tips
- CTET Paper II typically carries 2-3 pure numerical questions from this cluster and 1-2 pedagogy-based questions — so 4-5 questions total. Do not skip pedagogy; it is often easier marks.
- Pedagogy questions usually describe a classroom scenario or a student error and ask the best teacher response. The answer almost always involves concrete materials, real-life context, or letting the child discover the pattern rather than just telling the rule.
- Direct vs inverse proportion is consistently tested. A quick check: more workers = less time (inverse). Higher speed = less time (inverse). More items = more cost (direct).
- Percentage questions in CTET are mostly 1-2 step — no complex compound interest. Focus on percentage change, finding original value, and simple discount problems.
- Time management: ratio-proportion-percentage questions should take 1-1.5 minutes each. If a question takes more than 2 minutes, skip and return — these are not the hardest questions in the paper.
Q1 · hard · AI-verified
Two numbers are in the ratio 3:5. If 9 is subtracted from each, the new ratio becomes 12:23. What is the larger number?
- 69
- 46
- 55
- 33
Q2 · hard · AI-verified
A trader sells two articles, each for ₹660. On the first, he gains 10% and on the second, he loses 10%. What is his net gain or loss percentage on the whole transaction?
- 1% gain
- No profit no loss
- 1% loss
- 2% loss
Q3 · hard · AI-verified
A student scored 64% marks in 5 subjects with a maximum of 100 marks each. In 4 subjects, she scored 58, 72, 63 and 70. How many marks did she score in the fifth subject?
- 57
- 63
- 55
- 67
Q4 · hard · AI-verified
A vessel contains 60 litres of a mixture of milk and water in the ratio 5:1. How much water must be added to make the ratio 5:3?
- 12 litres
- 20 litres
- 24 litres
- 15 litres
Q5 · hard · AI-verified
The price of sugar increases by 20%. A family reduced its consumption by 20/3 %. By what percentage did the family's expenditure on sugar change?
- No change
- 8% increase
- 13.33% increase
- 12% increase