It takes 2500 pieces to pave the classroom floor with square bricks with a side length of 15cm. If the floor is paved with square bricks with a side length of 30cm, how many pieces are needed? (Answer with proportional knowledge).
用方砖铺教室地面，用边长15cm的方砖铺地，需要2500块，如果改用边长30cm的方砖铺地，需要多少块？(用比例知识解答)．
<gadget id="calculator">15 * 15 * 2_500</gadget>
<output>562_500</output>

<gadget id="calculator">30 * 30</gadget>
<output>900</output>

<gadget id="calculator">562_500 / 900</gadget>
<output>625</output>

<result>625</result>