Xiao Ming and grandma go upstairs together. There are 20 steps on each floor. Xiao Ming goes upstairs twice as fast as grandma. When Xiao Ming goes up to the 5th floor, how many floors does grandma still have?
小明和奶奶一起上楼，每层楼有20个台阶，小明上楼的速度是奶奶的2倍，小明上到5楼的时候，奶奶还在多少楼．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

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

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<result>3</result>