A playground has 100 people waiting in line before the gate opens. After the gate opens, the number of tourists coming every minute is the same. One entrance can accommodate 10 people per minute. If two entrances are opened, no one will queue up after 20 minutes. Now that there are 4 entrances open, no one will line up a few minutes after the doors open?
某游乐场在开门前已经有100人排队等候，开门后每分钟来的游客人数相同，一个入口处每分钟可以放入10人，如果开放2个入口，20分钟后就没有人排队了．现在开放4个入口处，那么开门后几分钟就没人排队了？
<gadget id="calculator">4 * 10</gadget>
<output>40</output>

<gadget id="calculator">20 * 10 * 2</gadget>
<output>400</output>

<gadget id="calculator">400 - 100</gadget>
<output>300</output>

<gadget id="calculator">300 / 20</gadget>
<output>15</output>

<gadget id="calculator">40 - 15</gadget>
<output>25</output>

<gadget id="calculator">100 / 25</gadget>
<output>4</output>

<result>4</result>