1. 

What is the speed of the boat in still water ?

I. The speed downstream of the boat is thrice the speed upstream.

II. The sum of the speeds of the boat, upstream and downstream is 12 kmph.

A. I alone sufficient while II alone not sufficient to answer
B. II alone sufficient while I alone not sufficient to answer
C. Either I or II alone sufficient to answer
D. Both I and II are not sufficient to answer
E. Both I and II are necessary to answer

Answer: Option B

Explanation:

Let the speed upstream be X km/hr. Then,

I. Speed downstream = 3X km/hr.

II. gives, speed of the boat in still water :

= (1/2 x 12 ) km/hr = 6 km/hr.

So, II only give the answer.

∴ Correct answer is (B).