Interview Q&A / Aptitude

1. A boat goes downstream at 15 km/h and upstream at 9 km/h. What are the speed of the boat in still water and the speed of the stream?

   Boat 12 km/h and stream 3 km/h. Downstream = b + s and upstream = b - s, so b = (15 + 9)/2 = 12 and s = (15 - 9)/2 = 3.

   BeginnerQuick answer1 min read
2. A swimmer covers 36 km downstream in 3 hours and 24 km upstream in 4 hours. Find the swimmer's speed in still water and the speed of the current.

   Swimmer 9 km/h and current 3 km/h. Downstream speed = 36/3 = 12 km/h, upstream = 24/4 = 6 km/h. Swimmer = (12 + 6)/2 = 9; current = (12 - 6)/2 = 3.

   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. A boat's speed in still water is 15 km/h. It goes 30 km upstream and returns in 4 hours 30 minutes. What is the speed of the stream?

   5 km/h. Solve 30/(15 - s) + 30/(15 + s) = 4.5. This gives 900/(225 - s^2) = 4.5, so 225 - s^2 = 200 and s = 5. Check: 30/10 + 30/20 = 3 + 1.5 = 4.5 hours.

   AdvancedQuick answer1 min read