Choose four non-repeating numbers from the five numbers 0, 1, 2, 7, and 9. What is the difference between the largest four-digit number and the smallest four-digit number?
从0，1，2，7，9五个数字中任选四个不重复的数字，组成的最大四位数和最小四位数的差是多少．
<gadget id="calculator">9_721 - 1_027</gadget>
<output>8_694</output>

<result>8_694</result>