If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 kmph, then the speed of the boat in still water is
Choose the correct choice from the following options.
A) 4.2 Km /hr B) 9 Km /hr C) 13 Km /hr D) 21 Km /hr E) None
Solution   Rate upstream	= (7/42x60)kmph   = 10 kmph.   Speed upstream	= 3 kmph.   Let speed in still water be x km/hr. Then,   speed upstream = (x - 3) Km/hr.   ∴ x - 3 = 10 or   ‹=›x = 13 Km/hr   Answer 13 Km /hr
<result>C</result>
If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 kmph, then the speed of the boat in still water is