Master Li has produced a batch of parts, 240 of which are 20 times less than the unfinished ones. How many parts are still left unfinished? (solution by equation)
李师傅生产一批零件，已做好240个，比未做的2倍少20个，还有多少个零件没有做？(用方程解)
<gadget id="calculator">20 + 240</gadget>
<output>260</output>

<gadget id="calculator">260 / 2</gadget>
<output>130</output>

<result>130</result>