(2/7) of a number is 30, what is (1/5) of this number.
一个数的(2/7)是30，这个数的(1/5)是多少．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">30 / (2/7)</gadget>
<output>105</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">105 * (1/5)</gadget>
<output>21</output>

<result>21</result>