A drum contains forty liters of whisky. Four liters of whisky is taken out and replaced by soda. This process is carried out twice further. How much whisky is now contained by the container?

**(A)** 30 Lt

**(B)** 29.16 Lt

**(C)** 28.70 Lt

**(D)** 27.60 Lt

**Answer:** **(B)** **Explanation:** **Hint: Suppose a solution contains x units of a liquid from which y units are taken out and replaced by water. After n repeated operations, quantity of pure liquid remaining in solution**

** =x(1−y/x) ^{n}=x(1−y/x)^{n} units.**

So, Whisky in the drum now

=40(1−4/40)^{3}=40(1−1/10)^{3}

=29.16

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