If it took 21 minutes to saw a piece of wood into 4 sections, how many minutes did it take to saw each time?
把一根木头锯成4段花了21分钟，则每锯一次花了多少分钟．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">21 / 3</gadget>
<output>7</output>

<result>7</result>