Aptitude - Average - Discussion

Average cost = 7.50/3 + 8/3 + 8.50/3.
Average cost = 2.50 + 2.66 + 2.83 = 7.99.

1st year = 4000/7.5 = 533.33 litres,
2nd year = 4000/8 = 500 litres,
3rd year = 4000/8.5 = 470.58 litres.

Total Petrol in 3 years = 1503.91 litres
Total amount invested in 3 year = 4000 * 3 = 12000,
Average cost of petrol per litre = 12000/1503.91 = 7.98 Rs.

To find the approximate average cost per litre of petrol over the three years, we can calculate the weighted average based on the amounts spent each year.

Let's break down the problem:

Year 1:
Cost per litre = Rs. 7.50
Amount spent = Rs. 4000

Year 2:
Cost per litre = Rs. 8
Amount spent = Rs. 4000

Year 3:
Cost per litre = Rs. 8.50
Amount spent = Rs. 4000.

Total amount spent over three years = 3 * Rs. 4000 = Rs. 12000,

Now, let's calculate the weighted average cost per litre:
Weighted average cost per litre = (Cost per litre in Year 1 * Amount spent in Year 1 + Cost per litre in Year 2 * Amount spent in Year 2 + Cost per litre in Year 3 * Amount spent in Year 3)/Total amount spent.

Weighted average cost per litre = (7.50 * 4000 + 8 * 4000 + 8.50 * 4000)/12000
Weighted average cost per litre = (30000 + 32000 + 34000)/12000
Weighted average cost per litre = 96000/12000,
Weighted average cost per litre = Rs. 8.

So, the approximate average cost per litre of petrol over the three years is Rs. 8.

Expenditure = price * consumption.

For
1st yr consumption = 4000/7.5 = 533.33 ltr.
2nd yr consumption = 4000/8 = 500 ltr.
3rd yr consumption = 4000/8.5 = 470.58 ltr.

Average consumption per yr = sum of all/3 = 501.307 ltrs.

Expenditure = price * consumption.
4000 = price * 501.307.
price = 4000/501.307 = 7.979139505.

Thanks for explaining @Arjun.

A car owner buys the petrol in 1st year will be = 4000/7.5 = 533.33 litres.
A car owner buys the petrol in 2nd year will be = 4000/8 = 500 litres,
A car owner buys the petrol in 3rd year will be = 4000/8.5 = 470.58 litres,
Total Petrol in 3 year will be = 1503.91 litre

Now the total amount invested in 3 year will be = 4000 * 3 = 12000.
So, the average cost of petrol per litre will be = 12000/1503.91 = 7.98 Rs (approx).

Thank you for explaining @Arvind Sahu.

Thanks @Krishna.

Thanks @Krishna.

Why can't we take the average of cost prices given? Please explain.