It takes 15 minutes to saw a 2-meter-long log into 0.5-meter sections; if it is sawed into 0.4-meter sections, how many minutes will it take?
把2米长的圆木锯成每段长0.5米，要15分钟；如果锯成每段0.4米，要多少分钟．
<gadget id="calculator">2 / 0.5</gadget>
<output>4</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<result>20</result>