From a 54-litre container of pure milk, 9 litres are removed and replaced by water. This process is repeated three times in total. What is the final quantity of milk left in the container?

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Accepted Answer

1. Each replacement leaves a fraction of milk $\dfrac{54-9}{54}=\dfrac{45}{54}=\dfrac{5}{6}$. 
2. After three repeats the fraction left is $(5/6)^3=125/216$. 
3. Milk left = $54	imes\dfrac{125}{216}=\dfrac{125}{4}=\mathbf{31.25}$ litres.

FINAL_ANSWER: b

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