Thrice the speed of a boat downstream is equal to four times the speed upstream. The ratio of its speed in still water to its speed in current is-

Question: Thrice the speed of a boat downstream is equal to four times the speed upstream. The ratio of its speed in still water to its speed in current is-

Solution:
Let,
Speed in still water = x km/hr.
Speed of current = y km/hr.
Speed downstream = (x + y) km/hr.
Speed upstream = (x - y) km/hr.
so,
3 (x + y) = 4 (x - y)
⇒ 3x + 3y = 4x - 4y
⇒ 4x - 3x = 3y + 4y
⇒ x = 7y
⇒ x/y = 7/1
∴ x : y = 7 : 1