Question

A taxi driver filled his car's petrol tank with $40$ litres of petrol on Monday. The next day, he filled the tank with $50$ litres of petrol. If the petrol costs $Rs.44$ per litre. How much did he spend on petrol ?

Answer 1

If petrol filled on the first day is $x$ and petrol filled on the second day is $y$ and the price of petrol for one litre is $p$ . Then the cost of petrol for quantity $x$ will be $p \times x$ and the cost of petrol for quantity $y$ will be $p \times y$ . Therefore, the total cost of petrol for both days is $py + px$ .

Complete step by step answer:
It is given that cost of petrol for $1$ litre $=$ $Rs.44$
A taxi driver filled his car petrol tank with $40$ litres on Monday. Therefore we can say that
Quantity of petrol filled on Monday $= {\text{ }}40L$
$\therefore$ Cost of $40L$ petrol $=$ cost of petrol per litre $\times$ Quantity of petrol filled on Monday
$= {\text{ Rs}}44{\text{ }} \times {\text{ }}40$
$= {\text{ Rs1760}}$
And the next day , on Tuesday he filled the tank with $50L$ of petrol. So, we can say that
Quantity of petrol filled on Tuesday $= {\text{ 50L}}$
$\therefore$ Cost of ${\text{50L}}$ petrol $=$ cost of petrol per litre $\times$ Quantity of petrol filled on Tuesday
$= {\text{ Rs}}{\text{.44 }} \times {\text{ 50}}$
$= {\text{ Rs}}{\text{.2200}}$
Therefore, the total cost of petrol he spend $= {\text{ Rs}}{\text{.2200 + Rs}}{\text{.1760}}$
$= {\text{ Rs}}{\text{.3960}}$

Note:
Note that the basic and practical idea to solve this question correctly is to read this question carefully because a minimal change in statement and values can make a huge difference in the final answer. So, reading and noting short points is the first and the basic step in this type of question. Like in this question if the per price is same for both days then we can apply a shortcut method to find the total cost and for this the shortcut method is that after adding the quantity of petrol of both days , multiply it with the cost of petrol given for one litre. On the other hand, if price varies on both days then multiply the quantities separately by the price given according to the days. Then add them to get the total cost of petrol.