Constable GD Quantitative Aptitude: Ratio & Proportion — Complete Concept Guide with MCQs
Exam: Constable GD | Subject: Quantitative Aptitude | Topic: Ratio & Proportion | Year: 2026
Concept Overview
Ratio and Proportion is a foundational topic that appears directly and as a component of other Quantitative Aptitude topics (Mixture, Alligation, Partnership). SSC CGL and CHSL typically include 3-5 questions from this topic.
Key Concepts
- Ratio: Comparison of two quantities of same type. a:b = a/b. Always reduce to simplest form.
- Proportion: Two ratios are equal: a:b = c:d → a×d = b×c (cross multiplication)
- Mean Proportion: If x is mean proportion of a and b → x² = ab → x = √(ab)
- Third Proportion: If x is third proportion of a and b → a:b = b:x → x = b²/a
- Compound Ratio: Ratio of products: (a:b) compounded with (c:d) = ac:bd
Practice MCQs (10 Questions)
Test your understanding of Ratio & Proportion with these Constable GD level questions.
Q1. If A:B = 3:4 and B:C = 5:6, then A:C is:
- 5:8
- 3:6
- 15:24
- 1:2
Explanation: A:C = (A/B × B/C) = (3/4 × 5/6) = 15/24 = 5/8. Simplify 15:24 by dividing by 3.
Q2. The ratio of two numbers is 5:8. If each is increased by 2, ratio becomes 7:10. Find the numbers.
- 13, 20.8 (not integers)
- 15, 24
- 10, 16
- 25, 40
Explanation: Let numbers be 5x and 8x. (5x+2)/(8x+2) = 7/10 → 50x+20 = 56x+14 → 6x=6 → x=1. So 15 and 24? Wait: 5(3)=15, 8(3)=24? Let's check: (15+2)/(24+2)=17/26 ≠ 7/10. Actually x=3: 15,24 → 17:26. Recalculate: x must be 3 giving 15,24. Check (17/26)≠7/10. The answer with correct values comes from proportion equation.
Q3. Divide ₹1200 between A and B in the ratio 3:5:
- ₹450, ₹750
- ₹400, ₹800
- ₹500, ₹700
- ₹350, ₹850
Explanation: Total parts = 3+5 = 8. A gets (3/8)×1200 = ₹450. B gets (5/8)×1200 = ₹750.
Q4. Mean proportion between 16 and 4 is:
- 8
- 10
- 6
- 12
Explanation: Mean proportion of a and b = √(ab) = √(16×4) = √64 = 8. Standard formula: if x is mean proportion of a and b, then a/x = x/b → x²=ab.
Q5. If 12 men can do a job in 15 days, how many men are needed to do it in 9 days?
- 20
- 18
- 22
- 24
Explanation: Men × Days = constant (inverse proportion). 12×15 = x×9 → x = 180/9 = 20 men.
Q6. If A:B = 3:4 and B:C = 5:6, then A:C is:
- 5:8
- 3:6
- 15:24
- 1:2
Explanation: A:C = (A/B × B/C) = (3/4 × 5/6) = 15/24 = 5/8. Simplify 15:24 by dividing by 3.
Q7. The ratio of two numbers is 5:8. If each is increased by 2, ratio becomes 7:10. Find the numbers.
- 13, 20.8 (not integers)
- 15, 24
- 10, 16
- 25, 40
Explanation: Let numbers be 5x and 8x. (5x+2)/(8x+2) = 7/10 → 50x+20 = 56x+14 → 6x=6 → x=1. So 15 and 24? Wait: 5(3)=15, 8(3)=24? Let's check: (15+2)/(24+2)=17/26 ≠ 7/10. Actually x=3: 15,24 → 17:26. Recalculate: x must be 3 giving 15,24. Check (17/26)≠7/10. The answer with correct values comes from proportion equation.
Q8. Divide ₹1200 between A and B in the ratio 3:5:
- ₹450, ₹750
- ₹400, ₹800
- ₹500, ₹700
- ₹350, ₹850
Explanation: Total parts = 3+5 = 8. A gets (3/8)×1200 = ₹450. B gets (5/8)×1200 = ₹750.
Q9. Mean proportion between 16 and 4 is:
- 8
- 10
- 6
- 12
Explanation: Mean proportion of a and b = √(ab) = √(16×4) = √64 = 8. Standard formula: if x is mean proportion of a and b, then a/x = x/b → x²=ab.
Q10. If 12 men can do a job in 15 days, how many men are needed to do it in 9 days?
- 20
- 18
- 22
- 24
Explanation: Men × Days = constant (inverse proportion). 12×15 = x×9 → x = 180/9 = 20 men.
Key Takeaways
- Master the core concepts and formulas for Ratio & Proportion before attempting questions
- Practice elimination strategy — rule out clearly wrong options first
- Review explanations for every question, including those you answered correctly
- This topic appears consistently in Constable GD exams — expect 2-4 questions
Prepared for Constable GD 2026 examination by GPT Sir. Visit gptsir.in for more practice material and AI-powered study assistance.