Master Wang processes a batch of parts, and the number completed on the first day is 20% of the total number of parts. If he processes 45 more parts, he can complete half of this batch of parts. How many parts are there in this batch?
王师傅加工一批零件，第一天完成的个数是零件总数的20%，如果再加工45个，就可以完成这批零件的一半．这批零件共有多少个？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/2) - (1/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">45 / (3/10)</gadget>
<output>150</output>

<result>150</result>