The No. 1 bus departs every 3 minutes, and the No. 3 bus departs every 5 minutes. These two buses depart at the same time, at least how many minutes later they depart at the same time.
第1路公交汽车每3分钟发一次车，第3路公交汽车每5分钟发一次车，这两路车同时发车，至少再过多少分钟又同时发车．
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<result>15</result>