"Story Book" is 20 yuan and 40 cents each, how much does it cost to buy 4 copies.
《故事书》每本20元4角，买4本要多少．
<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">20 + (2/5)</gadget>
<output>102/5 = around 20.4</output>

<gadget id="calculator">(102/5) * 4</gadget>
<output>408/5 = around 81.6</output>

<result>408/5 = around 81.6</result>