IBPS PO Quantitative Aptitude: Boats & Streams questions with solutions

Q1. A motor boat covers a certain distance downstream in 6 hours and the same distance upstream in 8 hours. If speed of stream = 2 km/h, find speed of boat in still water.

1. 20 km/h
2. 15 km/h
3. 23 km/h
4. 14 km/h

Answer: 14 km/h

Let boat speed=v km/h. Distance: 6(v+2)=8(v-2). 6v+12=8v-16. 2v=28. v=14 km/h.

Q2. A boat rows 18 km downstream and back in 8 hours. If speed doubled, same trip in 3.2 hours. Find speed of boat in still water.

1. 9 km/hr
2. 5 km/hr
3. 6 km/hr
4. 8 km/hr

Answer: 6 km/hr

Let b=boat speed, s=stream speed. Eq1: 36b/(b²-s²)=8 → s²=b²-9b/2. Eq2: 72b/(4b²-s²)=3.2 → 72b/(3b²+9b/2)=3.2 → 72/(3b+4.5)=3.2 → 3b=18 → b=6 km/hr.