A is (2/3) of b, (1/5) of c, and b is how much of c.
a是b的(2/3)，是c的(1/5)，b是c的多少．
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

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

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

<gadget id="calculator">1 / (2/3) / 5</gadget>
<output>3/10 = around 0.3</output>

<result>3/10 = around 0.3</result>