Master Li plans to make a batch of parts. If he makes 10 more parts per hour, he can complete the task 1 hour earlier; if he makes 20 more parts per hour, he can complete the task 1 hour earlier. Ask Master Li how many parts he plans to make?
李师傅计划做一批零件，如果他每小时多做10个，可提前1小时完成任务；如果他每小时再多做20个，则又可提前1小时完成任务．问李师傅计划做多少个零件？
<gadget id="calculator">2 / 30</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 30</gadget>
<output>2</output>

<gadget id="calculator">10 / 10</gadget>
<output>1</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) - (1/15)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<gadget id="calculator">30 + 10</gadget>
<output>40</output>

<gadget id="calculator">40 / 10</gadget>
<output>4</output>

<gadget id="calculator">30 * 4</gadget>
<output>120</output>

<result>120</result>