Multiple choice general knowledge math & puzzles A man can row upstream at 8 kmph and downstream at 13 kmph.The speed of the stream is ? 2.5 kmph 4.2 kmph 5 kmph 10.5 kmph Reveal answer Fill a bubble to check yourself A Correct answer Explanation Stream speed = (downstream speed - upstream speed) / 2 = (13 - 8) / 2 = 2.5 kmph. This formula works because downstream speed = boat speed + stream speed, while upstream speed = boat speed - stream speed. Subtracting eliminates boat speed and doubles the stream speed.