Correct Answer - Option 1 : 2 km/hr
Given:
Downstream distance = 24 km
Upstream distance = 24 km
Formula Used:
Speed = Distance/Time
D = B + S
U = B - S
where, D → Downstream speed, U → Upstream speed, B → Speed of the boat in still water, S → Speed of the stream.
Calculations:
24/D + 24/U = 14
⇒ 24/(B + S) + 24/(B - S) = 14
⇒ 24/(7 + S) + 24/(7 - S) = 14
⇒ [24 × (7 - S) + 24 × (7 + S)]/(7 + S) × (7 - S) = 14
⇒ 24 × 7 × 2/(49 - S2) = 14
⇒ 24 = 49 - S2
⇒ S2 = 49 - 24 = 25
⇒ S = 5 km/hr
U = (B - S)
⇒ U = (7 - 5)
⇒ U = 2 km/hr
∴ The upstream speed is 2 km/hr.