Divide 1 to 999 into 20 groups. It is known that the average of each of these 20 groups is equal. What is the average of this equality?
把1～999分成20组，已知这20组中每一组的平均数都相等，这个相等的平均数是多少．
<gadget id="calculator">1 + 999</gadget>
<output>1_000</output>

<gadget id="calculator">999 / 2 / 999</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1_000 * (1/2)</gadget>
<output>500</output>

<result>500</result>