The average volume of water in 13 bottles is 1.75 l. The volume of water in two other bottles are 1.45 l and 1.3 l. Find the average volume of water for all the 15 bottles.

Hi Xin,
Please find below the solution to the asked query :

$$\begin{gathered} \mathrm{We} \mathrm{have}, \\ \mathrm{average} \mathrm{volume} \mathrm{of} \mathrm{water} \mathrm{in} 13 \mathrm{bottles} = 1.75 \mathrm{l} \\ \Rightarrow \frac{\mathrm{total} \mathrm{amount} \mathrm{of} \mathrm{water} \mathrm{in} 13 \mathrm{bottles}}{13} = 1.75 \\ \Rightarrow \mathrm{total} \mathrm{amount} \mathrm{of} \mathrm{water} \mathrm{in} 13 \mathrm{bottles} = 13 \times 1.75 = 22.75 \mathrm{l} \\ \mathrm{Now}, \mathrm{amount} \mathrm{of} \mathrm{water} \mathrm{in} \mathrm{the} \mathrm{remaining} 2 \mathrm{bottles} = 1.45 + 1.3 = 2.75 \mathrm{l} \\ \mathrm{Now}, \mathrm{total} \mathrm{amount} \mathrm{of} \mathrm{water} \mathrm{in} 15 \mathrm{bottles} = 22.75 + 2.75 = 25.5 \mathrm{l} \\ \mathrm{Now}, \mathrm{average} \mathrm{volume} \mathrm{of} \mathrm{water} \mathrm{in} 15 \mathrm{bottles} = \frac{\mathrm{total} \mathrm{amount} \mathrm{of} \mathrm{water} \mathrm{in} 15 \mathrm{bottles}}{15} = \frac{25.5}{15} = 1.7 \mathrm{litres} \end{gathered}$$

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