A large classroom is 20 meters long and 10 meters wide. The floor is paved with square tiles with a side length of 5 decimeters. How many such tiles are needed?
一间大教室，长20米，宽10米，用边长是5分米的正方形瓷砖铺地，需要这样的瓷砖多少块？
<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">200 / (1/4)</gadget>
<output>800</output>

<result>800</result>