Multiple choice

A man swimming in a river flowing at 3km/hr, find that in a given time he can swim thrice as far downstream as he can swim upstream. What will be his speed in still water?

  1. 5 km/hr

  2. 6 km/hr

  3. 7 km/hr

  4. 8 km/hr
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let v be the speed in still water. Downstream speed is v+3, upstream is v-3. Given v+3 = 3(v-3), so v+3 = 3v-9, which means 2v = 12 or v = 6 km/hr.

AI explanation

Let the man's speed in still water be v kilometers per hour; his downstream speed is v + 3 and his upstream speed is v - 3. Since he swims thrice as far downstream as upstream in the same time, the equation is v + 3 = 3(v - 3). Solving gives v + 3 = 3v - 9, which means 12 = 2v and v = 6. His speed in still water is 6 km/hr.

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