Question

8 litres are drawn from a flask containing milk and then filled with water. The operation is performed 3 more times. The ratio of the quantity of milk left and total solution is $\frac{81}{625}$. How much milk the flask initially holds?

• A. 10 ltr
• B. 20 ltr
• C. 30 ltr
• D. 40 ltr
• E. None of these

Answer 1

The correct option is B 20 ltr

Let initial quantity be $Q$ and final quantity be $F$
$F=Q{(1-\frac{8}{Q})}^4\frac{81}{625}={(1-\frac{8}{Q})}^4\frac{3}{5}=\frac{1-8}{Q}$
$Q=20$