3. Two escalators are moving at the same speed: one going down, the other going up. Seventh-grader Semyon stepped onto the escalator going down and tried to climb up it, but with his usual effort, he could not move at all. At the moment Semyon stepped onto the adjacent escalator, he dropped his glove on the first step. But he did not notice it and walked up with the same speed. Where will the glove be when Semyon reaches the top?
3. Answer: Exactly at the midpoint of the escalator. Solution. Semyon tried to move up an escalator moving downwards and could not move from his spot. Therefore, Semyon's own speed is equal to the speed of the escalator. According to the problem, the escalators move at the same speed. Thus, when Semyon started to climb the escalator moving upwards, his speed was twice the "speed" of the glove, which moves at the speed of the escalator. At the moment Semyon reaches the top, the glove will have traveled exactly half the distance. Grading criteria: correct reasoning provided, correct answer obtained - 7 points. The conclusion that Semyon's own speed is equal to the speed of the escalator is made, but there is no further progress or it is incorrect - 2 points.