A boat can travel 60 km in 3 hours while going downstream, It can travel 90 km in 5 hours while going upstream. What is the ratio of the speed of the boat in still water to the speed of the stream?
downstream = $$\frac{distance}{time}$$
downstream = $$\frac{60}{3}$$
        =20km/hr
upstream= $$\frac{distance}{time}$$
upstream = $$\frac{90}{5}$$
   = 18km/hr
Speed of boat =$$\frac{speed\ of\ upstream+speed\ of\ downstream}{2}$$
 = 19km/hr
Speed of stream=$$\frac{speed\ of\ upstream-speed\ of\ downstream}{2}$$
 = 1km/hr
Ratio = $$19:1$$
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