- 128
- 34
- 43
- 126

Option 2 : 34

**Given:**

Quantity of pure milk = 162 litres

18 litres of milk is replaced by water 2 times.

**Formula used:**

Suppose a container contains A units of a liquid from which B units are taken out and replaced by water.

After n operations, operations, operations, operations,

Quantity of pure liquid in the final mixture = A {1 - (B/A)}^{n}

**Calculation:**

According to the question,

Quantity of pure milk in the final mixture = A {1 - (B/A)}^{n}

⇒ 162 × {1 - (18/162)}^{2}

⇒ 162 × {1 - (1/9)}^{2}

⇒ 162 × (8/9)^{2}

⇒ 162 × (64/81)

⇒ 128

Now, the quantity of water = 162 - 128 = 34

**∴ The quantity of water in the final mixture is 34 litres.**

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