Leng Qian accidentally lost the parentheses in the formula 30*(□+20) when copying homework; then the result of her calculation is much less than the correct result.
冷倩在抄作业时不小心把算式30*(□+20)中的括号弄丢了；那么她算的结果比正确结果少多少．
<gadget id="calculator">30 * 20</gadget>
<output>600</output>

<gadget id="calculator">600 - 20</gadget>
<output>580</output>

<result>580</result>