A boat goes 100 km downstream in 10 hours, and 75 m upstream in 15 hours. The speed of the stream is________?

A. 7 km/h
B. 5 km/h
C. 3 km/h
D. 2 (1/2) km/h
Explanation:
100 — 10 DS = 10
? —- 1
75 —- 15 US = 5
? —– 1 S = (10 – 5)/2
= 2 2 ½ kmph