A person has a chemical of Rs 15 per liter. In what ratio should water be mixed in that chemical so that after selling the mixture at Rs 12 per liter he may get a profit of 20%. किसी व्यक्ति के पास प्रति लीटर 15 रुपये का रसायन होता है। उस रसायन में किस अनुपात में पानी मिलाया जाना चाहिए ताकि मिश्रण को 12 रुपये प्रति लीटर पर बेचने के बाद उसे 20% का लाभ मिल सके।

Selling price is Rs 12 with 20% profit, so cost price of mixture = 12/1.2 = Rs 10 per liter. Chemical costs Rs 15/liter, so water (free) must be mixed to reduce average cost to Rs 10. Using alligation: (15-10):(10-0) = 5:10 = 1:2 (water:chemical). Wait - this gives chemical:water ratio. Correct calculation: let water:chemical = x:1, then (0x + 15*1)/(x+1) = 10, giving 15 = 10x + 10, so x = 0.5. This means water:chemical = 1:2 or chemical:water = 2:1.