Record the four-digit \overline{abcd} as X, and record the smallest four-digit number composed of its four numbers a, b, c, d as X*, if XX*=999, then such a four-digit number X How many are there?
记四位数\overline{abcd}为X，由它的四个数字a，b，c，d组成的最小的四位数记为X*，如果X-X*=999，那么这样的四位数X共有多少个．
<gadget id="calculator">8 * 6</gadget>
<output>48</output>

<result>48</result>