A boat covers a certain distance in one hour downstream with the speed of 10…

Concept

When a boat moves downstream (with the current), its effective speed over the ground is the boat's own still-water speed plus the current's speed: downstream speed = boat speed + current speed. Moving upstream (against the current) instead subtracts the current's speed. In both cases, distance covered = effective speed × time.

Application

1. Boat's still-water speed = 10 kmph; current's speed = 4 kmph.

2. Since the boat travels downstream, the effective (ground) speed = 10 + 4 = 14 kmph.

3. Time travelled = 1 hour, so distance = effective speed × time = 14 × 1 = 14 km.

Cross-check

Dividing the distance back by the time recovers the same speed: 14 km ÷ 1 hour = 14 kmph, which matches the downstream speed computed above. Also, since the current always helps a downstream trip, the resulting distance must be greater than what the boat alone would cover in still water (10 km) — 14 km is consistent with that check.

Source solution (reference image):