Correct Answer: Option A
Let the speed of the stream x mph. Then,
Speed downstream = (10+x) mph,
Speed Upstream =(10-x) mph.
So, 36/(10-x) – 36/(10+x)= 90/60
=> 72x × 60 = 90 (100-x2)
=> x2+48x-100=0
=> (x+50)(x-2)=0
=> x=2 mph.
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