Correct Answer - Option 3 : 2 km/h
Given:
Speed of a boat in still water = 14 km/h
Distance covered = 28 km
Time taken while doing downstream = 1 hour 45 minutes
Formulas used:
Speed downstream = Speed of boat + Speed of stream
Time = Distance/Speed
Calculation:
Let the speed of stream be = b
28 km/(14 + b) = 1 + 45/60 hours
⇒ 28/(14 + b) = 1 + 3/4
⇒ 28/(14 + b) = 7/4
⇒ 4/(14 + b) = 1/4
⇒ 14 + b = 4 × 4
⇒ 14 + b = 16
⇒ b = 16 - 14 = 2 km/h
∴ The speed of stream is 2 km/h.
