Subtract 7 from the third item 10 in the ratio 1:0.3=10:3, so how should the first item change, and the ratio still holds?
把比例1：0.3=10：3中的第三项10减去7，那么第一项应怎样变化，比例仍然成立？
<gadget id="calculator">10 - 7</gadget>
<output>3</output>

<gadget id="calculator">3 / 3</gadget>
<output>1</output>

<gadget id="calculator">0.3 * 1</gadget>
<output>0.3</output>

<gadget id="calculator">1 - 0.3</gadget>
<output>0.7</output>

<result>0.7</result>