One train leaves Chicago traveling at 45 miles per hour; another leaves New York traveling at 65 miles per hour. Both trains are accelerating at an even rate, though Qing’s 11:45 from Grand Central is newer than Russel’s 12:30. Hers has wifi, but they’re both reading books.

A common misconception about trains is that they all ride the same rails; two trains whose origins match each other’s destinations may, like packets, pick entirely distinct sets of nodes. Russel and Qing have a statistically even chance of passing each other as they kiss the southern edge of Erie.

When will they meet?