4) A boat covers 25km upstream and 44km downstream in 9 hours. Also it covers 15 km upstream and 22 km downstream in 5 hours. Find the speed of boat in still water.

Speed of boat in still water=8km/hr

Speed of stream=3km/hr

Step-by-step explanation:

Speed of boat in still water=x km/hr

Speed of stream=y km/hr

Speed of upstream=x-y km/hr

Speed of downstream=x+y km/hr

Let 1/(x-y)=a and 1/(x+y)=b

Time to go 25km up and 44 down=9

25a+44b=9>(1)

Time to go 15km up and 22km down=5

15a+22b=5>(2)

(2) × 2=> 30a+44b=10>(3)

(3)-(1)=>5a=1

a=1/5

1/(x-y)=1/5

x-y=5>(4)

Putting a=1/5 in (1),

5+44b=9

44b=4

b=1/11

1/(x+y)=1/11

x+y=11>(5)

(4)+(5)=>2x=16

x=8

y=3

Speed of boat in still water=8km/hr

Speed of stream=3km/hr