Question

The average monthly consumption of petrol for a car for the first 7 months of a year is 330 litres, and for the next 5 months is 270 litres. What is the average consumption per month during the whole year?

Answer 1

Average monthly consumption of petrol for the first 7 months = 330 litres
Average monthly consumption of petrol for the next 5 months = 270 litres
Sum of the monthly consumption of petrol for the first 7 months = $(330\times 7)\mathrm{litres}=2310\mathrm{litres}$
Sum of the monthly consumption of petrol for the next 5 months = $\left(270\times 5\right)\mathrm{litres}=1350\mathrm{litres}$

$$\begin{gathered} \therefore \mathrm{Average}\mathrm{consumption}\mathrm{of}\mathrm{petrol}\mathrm{per}\mathrm{month}\mathrm{during}\mathrm{the}\mathrm{whole}\mathrm{year}=\frac{2310+1350}{12} \\ =\frac{3660}{12} \\ =305\mathrm{litres} \end{gathered}$$

Therefore, the average consumption of petrol per month during the whole year is 305 litres.