The two brothers played by the circular pool with a circumference of 72 meters. They start from the same point and walk backwards, the elder brother travels 1.8 meters per second, and the younger one travels 1.2 meters per second. Think about at least the few times when they met, the meeting point happened to be the starting point?
兄弟二人在周长72米的圆形水池边玩．他们从同一点出发，背向而行，兄每秒行1.8米，弟每秒行1.2米．想一想他们至少第几次相遇时，相遇点正好是出发点？
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