3. Find the number of pairs of consecutive integers in the set $\{1000,1001,1002, \ldots, 2000\}$ such that no carrying is required when the two integers are added.
(1 mark)
3. 在集合 $\{1000,1001,1002, \ldots, 2000\}$ 中, 有多少對連續整數加起來時不用進位?