A hare and a tortoise start from point A at the same time, and cycle back and forth between places A and B, which are 500 meters apart. It is known that the speed of the rabbit is 40 meters per minute, and the speed of the tortoise is 60 meters per minute. How many times did they meet face to face in these half an hour?
兔子和乌龟同时从A地出发，在相距500米的A、B两地之间不断往返骑车．已知兔子的速度是每分钟40米，乌龟的速度是每分钟60米．在些发的半小时内，他们一共迎面相遇多少次．
<gadget id="calculator">40 + 60</gadget>
<output>100</output>

<gadget id="calculator">2 / 100</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">500 * (1/50)</gadget>
<output>10</output>

<gadget id="calculator">30 / 10</gadget>
<output>3</output>

<result>3</result>