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  1. If a boat goes 100 km downstream in 10 hours and 75 km upstream in 15 hours, then the speed of the stream is
    1. 2 km/hour
    2. 2·5 km/hour
    3. 3 km/hour
    4. 3·5 km/hour
Correct Option: B

As per the given in question ,

Rate downstream =
100
= 10 kmph
10

Rate upstream =
75
= 5 kmph
15

∴ Speed of current =
Rate downstream - Rate upstream
2

Speed of current =
1
(10 - 5) = 2.5 kmph
2

Aliter : Using Rule 1,
Here, p =
100
= 10 kmph
10

q =
75
= 5 kmph
15

Speed of Stream =
p - q
=
10 - 5
= 2.5 km/hr
22



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