There are 5 water inlet pipes installed in a pool, and it takes 7.5 hours to open the water inlet pipes 1, 2, and 3, 5 hours to open the water inlet pipes 1, 3, and 5, and 6 hours to open the water inlet pipes 1, 3, and 4 to fill a pool of water. Hours, it takes 4 hours to open the No. 2, No. 5, and No. 4 water inlet pipes. Ask how many hours it will take to fill the whole pool with five pipes.
一个水池安装有5个进水管要注满一池水打开1、2、3号进水管需要7.5小时，打开1、3、5号进水管需要5小时，打开1、3、4号进水管需要6小时，打开2、5、4号进水管需要4小时，问五管齐放注满全池需要多少小时．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / (1/3)</gadget>
<output>3</output>

<result>3</result>