Question

A speed of a boat in still water is 11km/hr. it can go a2 km upstream and return downstream to the original point in 2hrs 45 mins. find the speed of the stream

Answer 1

x=speed of stream
11+x=speed of boat downstream
11-x=speed of boat upstream
2 hr and 45 min=2.75 hr

time=distance/speed
12/(11+x)+12/(11-x)=2.75
Taking LCD
12(11-x)+12(11+x)=2.75(11+x)(11-x)
                             =2.75(121-x²)                             =332.75-2.75x²
132-12x+132+12x =332.75-2.75x²
264=332.75-2.75x²
2.75x²=332.75-264
           =68.75x²=68.75/2.75
x²=25x=5