Add (2/5) to a number, then subtract (1/4), the result is (17/20), what is the number? (solution by equation)
一个数加上(2/5)，再减去(1/4)，结果是(17/20)，求这个数是多少？(用方程解)
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">17 / 20</gadget>
<output>17/20 = around 0.85</output>

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

<gadget id="calculator">(17/20) - (2/5)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">(1/4) + (9/20)</gadget>
<output>7/10 = around 0.7</output>

<result>7/10 = around 0.7</result>