0.2+0.8*0.5-0.5=how much
0.2+0.8*0.5-0.5=多少
<gadget id="calculator">0.8 * 0.5</gadget>
<output>0.4</output>

<gadget id="calculator">0.4 - 0.5</gadget>
<output>-0.1</output>

<gadget id="calculator">0.2 + (-0.1)</gadget>
<output>0.1</output>

<result>0.1</result>