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5 km/hr
4 km/hr
3 km/hr
1km/hr
C. 3 km/hr
let rate upstream=x km/hr and rate downstream=y km/hr.
Then, 40/x +55/y =13… (i) and 30/x +44/y =10
Multiplying (ii) by 4 and (i) by 3 and subtracting, we get:11/y=1 or y=11.
Substituting y=11 in (i),we get:x=5.
Rate in still water =1/2(11+5)kmph=8kmph.
Rate of current=1/2(11-5)kmph=3kmph