4. A student correctly added the two two-digit numbers on the left of the board and got the answer 137. What answer will she obtain if she adds the two four-digit numbers on the right of the board?

A 13737
B 13837
C 14747
D 23723
E 137137
SolUTION
B

Since the sum of the two two-digit numbers $A B$ and $C D$ is 137 , the sum of the two-digit numbers $A D$ and $C B$ is also 137. Therefore the sum of the two four-digit numbers $A D C B$ and $C B A D$ is $(100 A D+C B)+(100 C B+A D)=100(A D+C B)+A D+C B=100 \times 137+137$ $=13700+137=13837$.