A boat can go 20km downstream and 30 km upstream in 2hours 20minutes.Also it can go 10km downstream and 8km upstream in 49minutes.What is the speed of boat downstream in km/h?

let speed of boat be 'b'
speed of stream be's'
speed upstream = b-s
speed downstream= b+s
now form 2 eqns using (b+s) and (b-s) and solve them
s= 2 kmph and b= 22 kmph
therefore, speed downstream= b+s = 24 kmph

Let,
speed downstream =x =speed of boat +speed of stream
speed upstream =y=speed of boat -speed of stream

Now form 2 equations in x and y by equating
Distance/Speed =Time

Solve for x and y