Chapter Exam

Chapter-7 Proportional Reasoning — Online MCQ Test

Q: If x and y are in direct proportion and x = 4 when y = 8, what is the constant of proportionality?

Answer: B. 2 — In direct proportion, y = kx, so k = y/x = 8/4 = 2.

Q: Which of the following represents an inverse proportion?

Answer: C. xy = 10 — In inverse proportion, the product of two variables is constant (xy = k), which is represented by xy = 10.

Q: If y is inversely proportional to x and y = 24 when x = 3, find y when x = 8.

Answer: A. 9 — In inverse proportion, xy = k. So k = 3 × 24 = 72. When x = 8, y = 72/8 = 9.

Q: If p and q are inversely proportional, and p = 6 when q = 8, find q when p = 12.

Answer: B. 4 — In inverse proportion, pq = k. So k = 6 × 8 = 48. When p = 12, q = 48/12 = 4.

Q: If the ratio of A to B is 3:4 and the ratio of B to C is 5:6, find the ratio A:B:C. (Pro level)

Answer: A. 15:20:24 — A:B = 3:4 and B:C = 5:6. To combine, make B equal: A:B = (3×5):(4×5) = 15:20 and B:C = (5×4):(6×4) = 20:24. Thus A:B:C = 15:20:24.

MATHS · Grade 8 · CBSE(NCERT)

Practice Chapter-7 Proportional Reasoning with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 8 MATHS. This chapter covers: direct proportion - inverse proportion - unitary method - constant of variation - ratios - comparing quantities. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter-7 Proportional Reasoning — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 8 MATHS — Chapter-7 Proportional Reasoning, with answers and explanations. These are sample questions; the exam has its own separate question set.

If x and y are in direct proportion and x = 4 when y = 8, what is the constant of proportionality?

A. 0.5
B. 2 ✓
C. 4
D. 8

Answer: B. 2
In direct proportion, y = kx, so k = y/x = 8/4 = 2.

Which of the following represents an inverse proportion?

A. y = 2x
B. y = x/2
C. xy = 10 ✓
D. x + y = 10

Answer: C. xy = 10
In inverse proportion, the product of two variables is constant (xy = k), which is represented by xy = 10.

If y is inversely proportional to x and y = 24 when x = 3, find y when x = 8.

A. 9 ✓
B. 64
C. 12
D. 72

Answer: A. 9
In inverse proportion, xy = k. So k = 3 × 24 = 72. When x = 8, y = 72/8 = 9.

If p and q are inversely proportional, and p = 6 when q = 8, find q when p = 12.

A. 2
B. 4 ✓
C. 16
D. 24

Answer: B. 4
In inverse proportion, pq = k. So k = 6 × 8 = 48. When p = 12, q = 48/12 = 4.

If the ratio of A to B is 3:4 and the ratio of B to C is 5:6, find the ratio A:B:C. (Pro level)

A. 15:20:24 ✓
B. 10:15:18
C. 5:8:12
D. 6:8:10

Answer: A. 15:20:24
A:B = 3:4 and B:C = 5:6. To combine, make B equal: A:B = (3×5):(4×5) = 15:20 and B:C = (5×4):(6×4) = 20:24. Thus A:B:C = 15:20:24.