If upstream speed =U and downstream speed =D, then speed of boat =(U+D)∕2 Calculation: According to the question, 20∕U+44∕D=8 15∕U+22∕D=5 Multiply by 2 the equation (ii) then subtract from 1 we get 20∕U+44∕D=8
30∕U+44∕D=10
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−10∕U=−2 ⇒U=5km∕hr Putting the value in equation (i), we get D=11 So, the speed of boat =(U+D)∕2=(5+11)∕2=8km∕hr ∴ The correct answer is 8km∕hr