A dairy blends two milk batches by fat content: Batch A: 75% fat, cost $1.20/L Batch B: 50% fat, cost $0.80/L They are mixed to obtain 60% fat milk and sells this mixture at $1.00/L. Assuming no other costs, what is the profit percentage on cost for the mixture?

Using the rule of alligation for the fat percentages, the ratio of Batch A to Batch B is (60 - 50) : (75 - 60), which is 10 : 15 or 2 : 3. The cost price per liter of the mixture is therefore (2 * 1.20 + 3 * 0.80) / 5, equaling \$0.96 per liter. Selling it at \$1.00 per liter gives a profit of $0.04, and the profit percentage is (0.04 / 0.96) * 100, which is 4.17%.

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