CMA Foundation · Fundamentals of Business Mathematics and Statistics · Ratios, Variations and Proportions
The monthly electricity cost C of a factory varies jointly with the number of machines M and the hours H run per day. When 8 machines run 6 hours a day, the cost is ₹24,000. What is the cost when 10 machines run 9 hours a day?
The cost is ₹45,000. With joint variation, cost equals a constant times machines times hours. The constant is 24,000 divided by 48, which is 500. Multiplying 500 by 10 machines and 9 hours gives ₹45,000.
- A₹45,000
- B₹40,000
- C₹56,250Correct
- D₹36,000
Explanation
C = k·M·H, so k = 24,000/(8×6) = 500. New cost = 500 × 10 × 9 = ₹45,000. Check: 24,000 × (10/8) × (9/6) = 24,000 × 1.25 × 1.5 = 45,000. Hence the correct value is ₹45,000, which is the option listed first.
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