There are 10 concert tickets with consecutive numbers. How many different ways are there to take 2 tickets with consecutive numbers?
有10张连号的音乐会入场券，要从中拿2张连号的券，一共有多少种不同的拿法．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<result>9</result>