A's number is 21, B's number is 30, how much less is A's number than B's number.
甲数是21，乙数是30，甲数比乙数少多少．
<gadget id="calculator">30 - 21</gadget>
<output>9</output>

<gadget id="calculator">9 / 30</gadget>
<output>3/10 = around 0.3</output>

<result>3/10 = around 0.3</result>