Ravi rows in a river where the downstream speed is 9 km/h and the upstream speed is 5 km/h. Find Ravi’s speed in still water and the speed of the current. (Give both in km/h.)

Introduction / Context:
Problems on boats and streams typically give downstream and upstream speeds to infer the speed in still water (boat speed) and the speed of the current. Downstream means the current helps the boat, upstream means the current opposes it.

Given Data / Assumptions:

• Downstream speed = 9 km/h
• Upstream speed = 5 km/h
• Let boat speed in still water be b (km/h) and current speed be c (km/h).

Concept / Approach:
Use the identities: downstream = b + c and upstream = b − c. Solve the two linear equations to find b and c.

Step-by-Step Solution:

Verification / Alternative check:
Check: downstream b + c = 7 + 2 = 9 km/h, upstream b − c = 7 − 2 = 5 km/h, which matches the data.

Why Other Options Are Wrong:
Options with 8 km/h or 3 km/h for the current violate b + c = 9 and b − c = 5 simultaneously; they do not satisfy both equations.

Common Pitfalls:
Mixing up b and c, or averaging 9 and 5 incorrectly for c. The average (9 + 5)/2 gives b, not c. The half-difference (9 − 5)/2 gives c.

Final Answer:
Speed in still water = 7 km/h; speed of current = 2 km/h.