Which information are sufficient to answer the questions? What is the speed of the stream? I. The ratio of speed in upstream to the speed in downstream is 2 : 3. II. The distance travelled in upstream in 2 hours by a man is more than distance travelled by him in downstream in 1 hour by 4 km.

For stream speed: I gives ratio upstream:downstream = 2:3. If boat=b, stream=s, then (b-s)/(b+s)=2/3, giving b=5s. Not sufficient alone (2 variables, 1 equation). II gives: 2(b-s) = 1(b+s) + 4, giving b-3s=4. Not sufficient alone. Both together: substitute b=5s into b-3s=4, giving 2s=4, s=2 km/h. Both statements together are sufficient.