Correct Answer - Option 3 : 13.55
Calculation :
Initial Quantity 'x' = 50
Replacement Quantity 'y' = 5
Number of process done 'n' = 3
Using formula,
\(Pure\;Quanity = Initial\;Q.\; \times \;{\left( {1 - \frac{{Replaced\;Q.\;}}{{Initial\;Q.}}} \right)^{No.\;of\;process\;done}}\)
\( = X \times {\left( {1 - \frac{Y}{X}} \right)^N}\)
Pure remaining milk = 50 × 9/10 × 9/10 × 9/10 = 36.45 litres
Then, water = 50 - 36.45 = 13.55 litres
Use fraction and power very carefully.