The floor of the classroom is 15 meters long and 5 meters wide, and the classroom floor is paved with square bricks with a side length of 0.5 meters. How many such floor tiles should be used at least?
教室地面长15米、宽5米，用边长是0.5米的方砖铺这个教室地面，至少要用多少块这样的地砖？
<gadget id="calculator">0.5 * 0.5</gadget>
<output>0.25</output>

<gadget id="calculator">5 / 0.25</gadget>
<output>20</output>

<gadget id="calculator">15 * 20</gadget>
<output>300</output>

<result>300</result>