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A boat goes downstream at a speed of 18 km/hr and upstream at a speed of 'm' km/hr. The boat travelled 90 km downstream in a river and then returned back taking altogether 12.5 hours. Then which of the following are true ?

A. m=12m = 12

B. m=15m = 15

C. Speed of water current is 3 km/hr

D. Speed of water current is 1.5 km/hr

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 3

9018+90m=12.5\dfrac{90}{18}+\dfrac{90}{m}=12.5 gives 90m=7.5\dfrac{90}{m}=7.5, so m=12m=12.

Current speed =18−122=3=\dfrac{18-12}{2}=3 km/hr.

So A and C are true.

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