Bunuel
A milkman cheats his customers by adding water to the milk he sells. He starts the day with 1000 litres of milk. However, after selling every 500 litres of milk, he adds and equal quantity of water to what he already has. The milkman can get away by cheating as long as the milk to water ratio does not fall below 1:7. He sells off all the milk if any addition of water will make the ratio fall below 1:7. Each customer buys exactly2 litres of milk a day from him. What is the total number of customers the milkman has cheated if he ends upselling all the milk ?
(A) 7550
(B) 7500
(C) 5500
(D) 1500
(E) 1000
Because we refill 500 L water (or after taking away 500 L of the liquid), the milk to total volume ratio is decreased by \(\frac{500}{1000} = \frac{1}{2}\) every time we refill (hence multiply by 50% every time).
After 1st refill, we have Milk:Total = 1:2, and after the 2nd refill we have Milk:Total = 1:4 etc.
We do not want to fall below Milk:Total of = 1:8. After the 3rd refill we hit 1:8 exactly. Therefore we can refill 3 times, which means we can use up 500*4 = 2000 L of milk. Then we can get away with cheating 2000/2 = 1000 customers.
Ans: E