1967 AHSME Problem 1

The three-digit number 2a3 is added to the number 326 to give the three-digit number 5b9. If 5b9 is divisible by 9, then a+b equals

\text{(A)}\ 2\qquad\text{(B)}\ 4\qquad\text{(C)}\ 6\qquad\text{(D)}\ 8\qquad\text{(E)}\ 9

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.