Ex. 5. In a stream running at 2 km/hr, a motor boat goes 10 km upstrea

1.	Ex. 5. In a stream running at 2 km/hr, a motor boat goes 10 km upstreamandback again to the starting point in 55 minutes. Find the speed of themotorboat in still water.
Answer» Let the speed of the boat in still water be x km/hr. Speed down stream =(x+2)km/hr Speed upstream =(x−2)km/hr Time taken to row 10 kms and back = =(10x+2+10x−2)hr 10x+2+10x−2=5560 12×10(x+2+x−2)=11(x2−4) 11x2−240x−44=0 (x−22)(11x+2)=0 x-22 = 0, x = 22 Speed of the boat in still water = 22 km/hr.

Ex. 5. In a stream running at 2 km/hr, a motor boat goes 10 km upstreamandback again to the starting point in 55 minutes. Find the speed of themotorboat in still water.

Answer»

Let the speed of the boat in still water be x km/hr.

Speed down stream =(x+2)km/hr

Speed upstream =(x−2)km/hr

Time taken to row 10 kms and back = =(10x+2+10x−2)hr

10x+2+10x−2=5560

12×10(x+2+x−2)=11(x2−4)

11x2−240x−44=0

(x−22)(11x+2)=0

x-22 = 0, x = 22

Speed of the boat in still water = 22 km/hr.