The average of the three numbers A, B, and C is 270, the number of A is 310, the number of B and the number of C are equal, what is the number of B?
甲、乙、丙三个数的平均数是270，甲数是310，乙数和丙数相等，乙数是多少．
<gadget id="calculator">270 * 3</gadget>
<output>810</output>

<gadget id="calculator">810 - 310</gadget>
<output>500</output>

<gadget id="calculator">500 / 2</gadget>
<output>250</output>

<result>250</result>