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. 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
3. A boat takes twice as long to go upstream as to cover the same distance downstream. What is the ratio of the boat's speed in still water to the speed of the stream?

   3 : 1. Same distance and double the time means the downstream speed is twice the upstream speed: b + s = 2(b - s), so b = 3s.

   IntermediateQuick answer1 min read
4. Ten years ago, A was half as old as B. If the ratio of their present ages is 3 : 4, what is the sum of their present ages?

   35 years. Present ages 3x and 4x. Ten years ago: 3x - 10 = (4x - 10)/2, so 6x - 20 = 4x - 10 and x = 5. Ages are 15 and 20.

   IntermediateQuick answer1 min read