5-(1/5)X=0.6X: 4(4/9)=4.5: 2, 1.2X-0.5X=1.2*(1/4).
5-(1/5)X=0.6X：4(4/9)=4.5：2,1.2X-0.5X=1.2*(1/4)．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1.2 * (1/4)</gadget>
<output>0.3</output>

<gadget id="calculator">0.3 / 0.7</gadget>
<output>0.428571</output>

<result>0.428571</result>