There are 3,000 rabbits in the farm, of which white rabbits account for 20% of the total. If some gray rabbits are sold, the number of white rabbits will account for 40% of the total number of existing rabbits. Ask how many gray rabbits are sold?
饲养场养有3000只兔子，其中白兔占总数是20%，如果卖掉一些灰兔，那么白兔只数占现有兔子总数的40%．问卖掉多少只灰兔？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

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

<gadget id="calculator">3_000 * (1/2)</gadget>
<output>1_500</output>

<gadget id="calculator">3_000 - 1_500</gadget>
<output>1_500</output>

<result>1_500</result>