Multiple choice

The ratio of downstream speed to upstream speed of a boat is 5 : 2. If the speed of the water in the stream decreases by 1 km/hr, the ratio changes to 3 : 2. Find the speed of the boat in still water.

  1. 35 4 km/hr

  2. 35 8 km/hr

  3. 5 km/hr

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the still-water speed be u and the original stream speed be v. From (u + v)/(u - v) = 5/2, u = 7v/3; using the changed ratio after the stream slows by 1 gives v = 15/8 and u = 35/8 km/hr.

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