A boat goes a distance of 3 km upstream and $4\frac{1}{2}$km downstream in 45 minutes, while it goes 3.6 km upstream and 2.4 Ans km downstream in 39 minutes. The speed (in km/h) of the boat when going downstream is:

12

We know that,

Upstream speed = (x - y) km/hr

Downstream speed = (x + y) km/hr

Let speed of boat and stream be x km/hr and y km/hr,

According to the question

= \(\frac{3}{(x - y)}\)+ \(\frac{4.5}{(x + y)}\)= \(\frac{45}{(60)}\)--- (A)

= \(\frac{3.6}{(x - y)}\)+ \(\frac{2.4}{(x+ y)}\)= \(\frac{39}{(60)}\)      --- (B)

After multiply by 1.2 in equation (A) subtract equation (B) from equation (A)

= \(\frac{3}{(x + y)}\) = \(\frac{1}{4}\)

= x + y = 12 km/hr