The ratio of the speed of stream of river and the speed of boat in still water is 2 : 5. The ratio of the speed of same stream and speed of another boat in still water is 3 : 4. What is the ratio of both the boat in still water?

15 : 8

Ratio of speed :-

 Boat(A)    :     Stream     :     Boat (B)

      5        :        2

                         3            :        4

-------------------------------------------------------

     15       :        6            :        8

Ratio of speed:

Boat (A)  :  Boat (B) = 15     :     8