DD.11 Number of steps to catch up

While Taro takes four steps forward, Jiro takes five steps forward.
Jiro goes to the distance by three steps where Taro goes by two steps.
When Jiro started and walked 200 steps, Taro pursues Jiro.
How many steps does Taro take to catch up Jiro ?

Answer
800 steps

Solution
Speed is described by (length of one step) × (number of steps of a definite period of time).
Since Jiro goes the distance by three steps which Taro goes by two steps, the length of one step of Jiro is 2 when that of Taro sets to 3.

Since Jiro takes five steps forward with the lenght of step 2 while Taro takes four steps forward with the lenght of step 3, the ratio of speed of Taro and Jiro is (3 × 4) : (2 × 5) = 12 : 10 = 6 : 5.

Since the ratio of the speed of Taro and Jiro is 6 : 5, the ratio of the distance which moving forward in same time is also 6 : 5.
When Taro catches up with Jiro, the distance Taro moved is 6 and that Jiro moved is 5.
The difference of 1 (= 6 - 5) will be 200 steps which is the distance Jiro moved at first.

The number of steps which Jiro moved before being caught is 1200 steps (200 steps × 6).
Since Taro goes the distance where Jiro goes by three steps by two steps, Taro takes 800 steps moving the distance where Jiro takes 1200 steps (1200 steps / 3 × 2).