Calculate with a simple method: 1990*198.9-1989*198.
用简便方法计算：1990*198.9-1989*198．
<gadget id="calculator">1_990 * 198.9</gadget>
<output>395_811</output>

<gadget id="calculator">1_989 * 198</gadget>
<output>393_822</output>

<gadget id="calculator">395_811 - 393_822</gadget>
<output>1_989</output>

<result>1_989</result>