If the base of a triangle increases (1/5) and the height decreases (1/5), then the reduced area is equal to the original area.
一个三角形的底增加(1/5)，高减少(1/5)，则减少面积是原来面积的多少．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(6/5) * (4/5)</gadget>
<output>24/25 = around 0.96</output>

<gadget id="calculator">1 - (24/25)</gadget>
<output>1/25 = around 0.04</output>

<result>1/25 = around 0.04</result>