Physics

Grade-9

Easy

Question

# Your heating system is 45 percent energy efficient. The total useful output energy is 9000 kWh.

Changing the insulation would increase your house to 85 percent energy efficient. The cost to change the insulation is 131776 Rs. The cost of heating is 7 Rs/ kWh. How much time will it take to recover your investment?

- 2 years
- 2 minutes
- 2 days
- 2 months

Hint:

### 2 years

## The correct answer is: 2 years

### 45 = (9000/X) × 100

X = 20,000.

Cost = 20,000 × 7 = 1,40,000

Moving forward to the part B which is 85%.

X = (9000 × 100)/85

X = 10,588

Cost = 10,588 × 7 = 74,116

Cost savings = 1,40,000 - 74,116 = 65,884

Cost to change the insulation = 1,31776

Time = 1,31,176/65,884 = 1.99 years

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