There is a pool, some water is kept at the bottom of the pool, and there is a spring that keeps gushing out. In order to drain the water in the pool, 9 water pumps were transferred in the original plan, which saved 8 hours compared with the original plan. The engineers calculated that if 10 water pumps were initially transferred, 12 hours would be saved compared to the original plan. In this way, after the water in the pool is drained, in order to keep the pool without water, at least how many pumps should be left.
有一个水池，池底存了一些水，并且还有泉水不断涌出．为了将水池里的水抽干，原计划调来了9台抽水机，这样比原计划节省了8小时．工程师们测算出，如果最初调来10台抽水机，将会比原计划节省12小时．这样，将水池的水抽干后，为了保持池中始终没有水，还应该至少留下多少台抽水机．
<gadget id="calculator">80 - 12 - 64</gadget>
<output>4</output>

<gadget id="calculator">720 - 120 - 576</gadget>
<output>24</output>

<gadget id="calculator">4 / 24</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / (1/6)</gadget>
<output>6</output>

<result>6</result>