Chapter-7 Proportional Reasoning — Online MCQ Test
MATHS · Grade 8 · CBSE(NCERT)
Practice Chapter-7 Proportional Reasoning with a free chapter-wise online MCQ test.
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.
Chapter-7 Proportional Reasoning — Important Questions & Answers
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.
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.
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.
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.
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.
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.