There are two boxes of chess pieces, A and B. There are 2700 pieces in box A, 30% of which are black pieces; there are 1200 pieces in box B, 90% of which are black pieces. Now take some chess pieces from box B and put them into box A. At this time, the sunspots in box A account for 40%, and the sunspots in box B still account for 90%. Ask how many chess pieces were taken from box B and put into box A?
有甲、乙两盒棋子，甲盒中有2700枚棋子，其中黑子占30%；乙盒中有1200枚棋子，其中黑子占90%．现在从乙盒中取出若干棋子放入甲盒中，此时甲盒中黑子占40%，乙盒中黑子仍占90%．问从乙盒中拿了多少枚棋子放入甲盒？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">2_700 * (3/10)</gadget>
<output>810</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1_200 * (9/10)</gadget>
<output>1_080</output>

<gadget id="calculator">810 + 1_080</gadget>
<output>1_890</output>

<gadget id="calculator">2_700 + 1_200</gadget>
<output>3_900</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3_900 * (2/5)</gadget>
<output>1_560</output>

<gadget id="calculator">1_890 - 1_560</gadget>
<output>330</output>

<gadget id="calculator">(9/10) - (2/5)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">330 / (1/2)</gadget>
<output>660</output>

<gadget id="calculator">1_200 - 660</gadget>
<output>540</output>

<result>540</result>