任选1和9998之间的两个不同的数，他们所包含的数字完全相同（0除外），如1000和1，1234和4231。用其中的大数，减去小数，得到结果R。从结果R中移出一个非零的数字。如果剩下的数字个数少于3，则在前补0，使得其至少包含3个数字。可以证明，如果给定剩下的3个数字，那么，可以确定被移去的那个数字。

如：

给定数字：“087”，可以确定，被移去的数字为3。因为4321-1234=3087，移去3，剩下087。

给定数字：“099”，可以确定，被移去的数字为9。因为1000-1=999，移去9，剩下099。

给定数字：“191”，可以确定，被移去的数字为7。因为4525-2554=1971，移去7，剩下191。-Choose between 1 and 9998 two different numbers, they contain exactly the same number (except 0), such as 1000 and 1,1234 and 4231. With large numbers of them, minus the decimal to get the result R. R removed from the result of a non-zero number. If the remaining number of digits less than 3, the first fill 0, making it at least three digits. Can be shown that if given the remaining three figures, then, can determine that the figure was removed.

Such as:

Given numbers: "087", can confirm the figures were removed 3. For 4321-1234 = 3087, removed 3, and the remaining 087.

Given numbers: "099", can confirm the figures were removed 9. As 1000-1 = 999, 9 removed, leaving 099.

Given numbers: "191", can confirm the figures were removed 7. For 4525-2554 = 1971, 7 removed, leaving 191.