In a pool, there is a water inlet pipe and a drain pipe. Open the water inlet pipe alone for 30 minutes to fill the pool, and open the drain pipe for 50 minutes to drain all the water in the pool. How many minutes will it take to fill the pool if both pipes are on?
一个水池里，有一个进水管和一个排水管，单开进水管30分钟将水池注满，单开排水管50分钟将满池水全部放完．如果两管齐开多少分钟将水池注满？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/30) - (1/50)</gadget>
<output>1/75 = around 0.013333</output>

<gadget id="calculator">1 / (1/75)</gadget>
<output>75</output>

<result>75</result>