Four students go rowing in the park, only 2 people can sit at a time, how many ways can they sit?
四个同学到公园划船，一次只能坐2人，有多少种坐法．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<result>6</result>