$1 \cdot 50$ An ordered pair of non-negative integers $(m, n)$ is called "simple" if no carrying is required when performing the addition $m+n$, and $m+n$ is called the sum of the ordered pair $(m, n)$. Find the number of "simple" ordered pairs of non-negative integers whose sum is 1492.
[Solution] The unit digits of $m, n$ can be 2, 0; 1, 1; 0, 2, three possibilities.
Similarly, the tens digit has ten possibilities, the hundreds digit has five, and the thousands digit has two.
Therefore, the number of possibilities is $3 \times 10 \times 5 \times 2=300$.