A and B compete to climb stairs, and A's speed is twice that of B's. When A reaches the 9th floor, how many floors does B reach?
甲乙两人比赛爬楼梯，甲的速度是乙的2倍，当甲跑到9层时，乙跑到了几层？
<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>