A car owner buys petrol at 7.50, 8.00 and 8.50 per litre for three successive years. What approximately is his average cost per litre of petrol if he spends 4000 each year?

Options

A. 8
B. 9
C. 7.98
D. `8.50`

Answer

To solve the problem of finding the average cost per litre of petrol over three years, we can follow these steps:

### Step 1: Calculate the quantity of petrol consumed each year.
The car owner spends 4000 each year on petrol, and the prices per litre for the three years are as follows:
- Year 1: 7.50 per litre
- Year 2: 8.00 per litre
- Year 3: 8.50 per litre

We can calculate the quantity of petrol consumed in each year using the formula:
\[ \text{Quantity} = \frac{\text{Amount spent}}{\text{Price per litre}} \]

For Year 1:
\[ \text{Quantity}_1 = \frac{4000}{7.50} = \frac{4000}{7.5} = 533.33 \text{ litres} \]

For Year 2:
\[ \text{Quantity}_2 = \frac{4000}{8.00} = 500 \text{ litres} \]

For Year 3:
\[ \text{Quantity}_3 = \frac{4000}{8.50} = \frac{4000}{8.5} \approx 470.59 \text{ litres} \]

### Step 2: Calculate the total quantity of petrol consumed over three years.
Now, we sum up the quantities consumed in each year:
\[ \text{Total Quantity} = \text{Quantity}_1 + \text{Quantity}_2 + \text{Quantity}_3 \]
\[ \text{Total Quantity} = 533.33 + 500 + 470.59 \approx 1503.92 \text{ litres} \]

### Step 3: Calculate the total amount spent over three years.
The total amount spent over three years is:
\[ \text{Total Amount} = 3 \times 4000 = 12000 \text{ rupees} \]

### Step 4: Calculate the average cost per litre of petrol.
The average cost per litre is calculated using the formula:
\[ \text{Average Cost} = \frac{\text{Total Amount}}{\text{Total Quantity}} \]
\[ \text{Average Cost} = \frac{12000}{1503.92} \approx 7.98 \text{ rupees} \]

### Final Answer:
The average cost per litre of petrol over the three years is approximately **7.98 rupees**.

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