When cleaning the classroom before school starts, Xiaoming can finish cleaning in 30 minutes; Xiaofen takes 50 minutes to finish cleaning. Now Xiaoming cleans for 6 minutes first, and then Xiaofen also joins in cleaning, so how many minutes will it take to finish cleaning.
开学前打扫课室，小明30分钟能打扫完毕；小芬却要50分钟才能打扫完毕．现在小明先打扫6分钟，然后小芬也来参加一起打扫，那么，还要多少分钟就可以打扫完毕．
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/30) * 6</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">(1/30) + (1/50)</gadget>
<output>4/75 = around 0.053333</output>

<gadget id="calculator">(4/5) / (4/75)</gadget>
<output>15</output>

<result>15</result>