There is a ship going back and forth between upstream and downstream of a certain river.
The speed of the ship is fixed when moving with no flow of the river.
The time of going up a river is twice of the time of going down.
When the speed of this ship is to be double, find the time ratio of going up and down.
Answer
7 : 5
Solution
The time ratio of going up and down is 2:1.
Answer
7 : 5
Solution
The time ratio of going up and down is 2:1.
Then the speed ratio of going up and down is 1:2.
In this case the speed of flow of the river is expressed as (2 - 1)/2 = 0.5 and the speed of the ship with no flow is 2 - 0.5 = 1.5.
When this speed is made double, it's 1.5 × 2 = 3.
The speed ratio of going up and down is (3 - 0.5) : (3 + 0.5) = 2.5 : 3.5 = 5 : 7.
