Buy 4 bottles of soda and get 1 free. 20 students want 1 bottle each. How many bottles of soda do you need to buy?
汽水买4瓶送1瓶，20名学生要每人1瓶，共需买多少瓶汽水．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">20 / (5/4)</gadget>
<output>16</output>

<result>16</result>