A car owner buys petrol at Rs.7.50, Rs. 8 and Rs. 8.50 per litre for three successive years. What approximately is the average cost per litre of petrol if he spends Rs. 4000 each year?

1Rs. 7.98
2Rs. 8
3Rs. 8.50
4Rs. 9

Answer:- 1

Explanation:-

Solution:

Total quantity of petrol consumed in 3 years

\begin{aligned} = (\frac{4000}{7.50} + \frac{4000}{8} + \frac{4000}{8.50}) litres \\ = 4000 (\frac{2}{15} + \frac{1}{8} + \frac{2}{17}) litres \\ = (\frac{76700}{51}) litres \\ Total amount spent \\ = R s . (3 \times 4000) \\ = R s . 12000. \\ ∴ Average Cost \\ = R s . (\frac{12000 \times 51}{76700}) \\ = R s . \frac{6120}{767} \\ = R s . 7.98 \end{aligned}

$\eqalign{ & = \left( {\frac{{4000}}{{7.50}} + \frac{{4000}}{8} + \frac{{4000}}{{8.50}}} \right){\text{litres}} \cr & = 4000\left( {\frac{2}{{15}} + \frac{1}{8} + \frac{2}{{17}}} \right){\text{litres}} \cr & = \left( {\frac{{76700}}{{51}}} \right){\text{litres}} \cr & {\text{Total}}\,{\text{amount}}\,{\text{spent}} \cr & = Rs.\,\left( {3 \times 4000} \right) \cr & = Rs.\,12000. \cr & \therefore {\text{Average}}\,{\text{Cost}} \cr & = Rs.\,\left( {\frac{{12000 \times 51}}{{76700}}} \right) \cr & = Rs.\,\frac{{6120}}{{767}} \cr & = Rs.\,7.98 \cr}$