The amount of water flowing into the reservoir is the same every minute. For example, if you turn on 5 faucets, the water will be drained in 2.5 hours. If you turn on 8 faucets, the water will be drained in 1.5 hours. Now, if you turn on 13 faucets, how many hours will it take to drain the water? ．
蓄水池每分钟流入的水量都相同，如打开5个水龙头，2.5小时把水放尽，如打开8个水龙头，1.5小时把水放尽，现打开13个水龙头，多少个小时把水放尽．
<gadget id="calculator">1 * 5 * 2.5</gadget>
<output>12.5</output>

<gadget id="calculator">1 * 8 * 1.5</gadget>
<output>12</output>

<gadget id="calculator">12.5 - 12</gadget>
<output>0.5</output>

<gadget id="calculator">2.5 - 1.5</gadget>
<output>1</output>

<gadget id="calculator">0.5 / 1</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 * 2.5</gadget>
<output>1.25</output>

<gadget id="calculator">12.5 - 1.25</gadget>
<output>11.25</output>

<gadget id="calculator">13 - 0.5</gadget>
<output>12.5</output>

<gadget id="calculator">11.25 / 12.5</gadget>
<output>0.9</output>

<result>0.9</result>