3 [Arithmetic. Mental arithmetic, etc.]

Having walked $4 / 9$ of the length of the bridge, the pedestrian noticed that a car was catching up to him, which had not yet entered the bridge. Then he turned back and met it at the beginning of the bridge. If he had continued his movement, the car would have caught up with him at the end of the bridge. Find the ratio of the car's speed to the pedestrian's speed.
From the condition, it follows that the time it takes for the car to approach the bridge is equal to the time it takes for the pedestrian to walk $4 / 9$ of the bridge. Therefore, if the pedestrian continues moving, by the time the car reaches the bridge, he will have walked ${ }^{8} / 9$ of the bridge. This means that in the time it takes for the car to drive across the bridge, the pedestrian manages to walk one-ninth of the bridge, so the speed of the car is 9 times greater than the speed of the pedestrian.

## Answer

9.