What is the monthly electricity bill for a house with m rooms and consuming n units ?
Consider the following for the next two (02) items that follow : The total monthly electricity bill for a house consists of the sum of two parts, one part is proportional to number of rooms and the other part is proportional to number of units consumed. ₹ 400 is the monthly electricity bill for a house with 8 rooms and consuming 240 units and ₹ 320 is the monthly electricity bill for a house with 6 rooms and consuming 200 units.
- A. ₹(40m+n)
- B. ₹(20m+n) ✓
- C. ₹\frac{40m+n}{2}
- D. ₹\frac{30m+n}{2}
Correct Answer: B. ₹(20m+n)
Explanation
Let the bill be C_1 \times \text{rooms} + C_2 \times \text{units}. We have 8C_1 + 240C_2 = 400 and 6C_1 + 200C_2 = 320. Solving this system of linear equations yields C_2 = 1 and C_1 = 20. Therefore, the bill for m rooms and n units is ₹(20m+n).
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