In what ratio must a mixture of 20% milk strength be mixed with that of 60% milk strength so as to get a new mixture of 25% milk strength?

Step 1: Understand the problem

• We have two milk mixtures: one with 20% milk and another with 60% milk.
• We want to mix them to get a mixture with 25% milk.

Step 2: Apply Alligation Rule

           60%      (higher strength)
             \      /
              \    /
               25% (desired)
              /    \
             /      \
           25 - 20 = 5
           60 - 25 = 35

Step 3: Ratio of Quantities

Higher : Lower = (25 - 20) : (60 - 25) = 5 : 35 = 1 : 7

Answer: 1 : 7

To obtain a mixture of 25% milk strength, the two mixtures (20% and 60%) must be mixed in the ratio 1:7 (60% : 20%).

This is a classic alligation and mixture problem, often seen in competitive exams. It demonstrates how to balance concentrations by using simple arithmetic differences to calculate the mixing ratio efficiently.