Ants on a stick
Four ants stand on a 100 cm stick, each crawling at 1 cm/s. Measured from the left end, they are at 10 cm (moving right), 30 cm (moving left), 70 cm (moving right), and 85 cm (moving left). Whenever two ants meet they instantly reverse directions; an ant that reaches either end falls off. How many seconds pass before the last ant falls off?
Show hints (2)+
- Two ants bouncing apart look exactly like two ants passing through each other - swap their labels.
- Then each ant walks a straight line; the last fall-off is the longest single walk to an end.
Answer
Reveal answer →Final answer
90
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