If (2/5)a=(4/7)b (both a and b are 0), then a:b=((())/(())).
如果(2/5)a=(4/7)b(a、b都不为0)，则a：b=((())/(()))．
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(4/7) / (2/5)</gadget>
<output>10/7 = around 1.428571</output>

<result>10/7 = around 1.428571</result>