A worker is sawing wood. It takes him 15 minutes to saw a long piece of wood into 4 sections. If the working speed remains constant, how many minutes will it take to saw each piece of wood into two sections?
一个工人锯木料，他用15分钟把一段长木料锯成了4段，如果保持工作速度不变，再把每段木料锯成两段，还需要多少分钟．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

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

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

<result>20</result>