A mixture of liters contains milk and water in the ratio of . A milkman mixes some more water in it and claim to sell it at cost price. If cost price of pure milk is Rs. and water is freely available and milkman made a total profit of on cost price of pure milk then find amount of water he mixed in the milk.
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This one took me a minute because I kept thinking the profit was on the original mixture cost. Once I set the milk quantity as the 'true cost' it clicked.
Same here. The wording about profit on cost price of pure milk is what tripped me up.
Yeah, I initially ignored the original water and got a weird number. Reading it carefully helps.
Can someone explain why we don't use the original 3 parts water in the final ratio? I know the milk stays constant but I'm second-guessing myself.
Original water is already there, but the question asks how much extra water he added. That's the trap.
Solid 655-705 for me. Not super hard once translated, but the profit wording makes it easy to lose time.
I got 40 by assuming milk cost is fixed and profit comes only from added water. Is that the same approach?
Basically yes. You just have to account for the fact that he sells the whole diluted mixture at the milk price.
What it tests
Your ability to reason about weighted averages and the composition of mixtures.
Common trap
Averaging the percentages of two solutions without weighting by their volumes.