How many ways are there to choose 2 people from 5 people and line up to take pictures?
从5个人中选2人排成一排照相，有多少种照法．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">5 * 2 * 2</gadget>
<output>20</output>

<result>20</result>