Interview Q&A / Aptitude

1. A 60-litre mixture has alcohol and water in the ratio 2 : 1. How much water must be added to make the ratio 1 : 2?

   60 litres. The mixture has 40 L alcohol and 20 L water. Alcohol stays 40 L, and for 1 : 2 water must be 80 L. So add 80 - 20 = 60 litres of water.

   BeginnerQuick answer1 min read
2. In what ratio should rice costing ₹40 per kg be mixed with rice costing ₹55 per kg to get a mixture worth ₹45 per kg?

   2 : 1. By alligation, cheaper : dearer = (55 - 45) : (45 - 40) = 10 : 5 = 2 : 1. Check: 2 kg at ₹40 plus 1 kg at ₹55 costs ₹135 for 3 kg, which is ₹45 per kg.

   BeginnerQuick answer1 min read
3. Two vessels contain milk and water in the ratios 3 : 1 and 5 : 3. If equal quantities from both are mixed, what is the ratio of milk to water?

   11 : 5. Milk fractions are 3/4 and 5/8. Taking one litre from each gives milk 3/4 + 5/8 = 11/8 litres out of 2, so milk is 11/16 and water 5/16 of the mixture.

   BeginnerQuick answer1 min read
4. ₹10,000 is lent partly at 8% and partly at 12% simple interest. The total interest for one year is ₹960. How much was lent at each rate?

   ₹6,000 at 8% and ₹4,000 at 12%. The overall rate is 960/10,000 = 9.6%. Alligation gives (12 - 9.6) : (9.6 - 8) = 2.4 : 1.6 = 3 : 2.

   IntermediateQuick answer1 min read
5. A milkman buys milk at ₹60 per litre. How much water should he add per litre so that by selling the mixture at ₹60 per litre he makes a 20% profit?

   200 ml per litre (milk : water = 5 : 1). For 20% profit at ₹60, the mixture's cost must be 60 / 1.2 = ₹50 per litre. Alligation of milk (₹60) and water (₹0) about ₹50 gives 50 : 10 = 5 : 1.

   IntermediateQuick answer1 min read
6. A 40-litre can is full of milk. 4 litres are taken out and replaced with water, and this is done three times in total. How much milk is left?

   29.16 litres. Each operation keeps (40 - 4)/40 = 0.9 of the milk, so after three rounds milk = 40 x 0.9^3 = 40 x 0.729 = 29.16 litres.

   AdvancedQuick answer1 min read