729 litres of a mixture contains sprit and water in the ratio 7 : 2. How much water is to be added to get a new mixture containing spirit and water in the ratio 7 : 3?

A 60 l

B 81 l

C 92 l

D 120 l

E None of these

Correct Answer: Option B

Spirit : water = 7 : 2

⇒ Spirit \(= \frac{7}{{7 + 2}} \times 729 = 567l\)

And, water = 729 – 567 = 162 litre

Now, let water mixed = ‘x’ litre

∴ According to the question –

⇒ 567/(162+x) = 7/3

⇒ x = 81 litres.

Hence, the required answer is 81 litre