The caterpillar and the ant ate a 640 mm long piece of bread from both ends. On the first day, the ant and the caterpillar each ate 20 mm. From the second day onwards, the caterpillar ate twice as fast as the previous day, and the ants ate every day. The speed of the bread is always (3/2) times that of the previous day, so how many days will it take for the ants and caterpillars to finish eating this bread?
小青虫和蚂蚁聪从两端吃一条640毫米长的面包，第一天蚂蚁和小青虫各自吃了20毫米，从二天其，小青虫每天吃的速度总是前一天的2倍，蚂蚁每天吃的速度总是前一天的(3/2)倍，那么，蚂蚁和小青虫吃完这个面包要多少天？
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