A scarf, if you sell it for 100 yuan, you can earn (1/4), if you sell it for 120 yuan, how much can you earn.
一条围巾，如果卖100元，可赚(1/4)，如果卖120元，可赚多少．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">100 / (5/4)</gadget>
<output>80</output>

<gadget id="calculator">120 - 80</gadget>
<output>40</output>

<gadget id="calculator">40 / 80</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>