Three containers A, B and C contains milk and water in ratio 4 : 1, 5 : 3 and 1 : 3. In what ratio they should mix together to make quantity of milk and water equal ?

Container A: milk:water=4:1 (milk=4/5=80%), Container B: 5:3 (milk=5/8=62.5%), Container C: 1:3 (milk=1/4=25%). For equal milk and water in final mixture, overall milk percentage should be 50%. Using alligation: Container A (80%) and C (25%) can mix to give 50% in ratio 25:30 or 5:6. Container B (62.5%) needs to balance with lower percentage containers. Testing option D (5:2:7): Total milk = 5*4/5 + 2*5/8 + 7*1/4 = 4 + 1.25 + 1.75 = 7; Total water = 5*1/5 + 2*3/8 + 7*3/4 = 1 + 0.75 + 5.25 = 7. Equal, so D is correct.