number of water inlet pipes are installed in a pool, and they inject equal amounts of water per minute. If you open 8 water inlet pipes, you can fill the pool according to the scheduled time. Now open several water pipes, and after (2/5) of the scheduled time, double the number of opened water pipes, and you can also fill the pool according to the scheduled time. ． So, how many water pipes were opened in total in the end?
一个水池安装若干根进水管，他们每分钟注水量相等．如果打开8根进水管，就能按预定时间注满水池，现在打开若干根水管，经过预定时间的(2/5)，再把打开的水管数增加1倍，也能按预定时间注满水池．那么，最后共打开水管多少根？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(2/5) * (1/8)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">2 * (1/8)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(2/5) * 2 * (1/8)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/4) - (1/10)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(1/20) + (3/20)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / (1/5)</gadget>
<output>5</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<result>10</result>