In arithmetic, rule-violation checking strategies are used while participants solve problems that violate arithmetic rules, like the five rule (i.e., products of problems including five as an operand end with either five or zero; e.g., 5 x 14 = 70) or the parity rule (i.e., when at least one of the two operands is even, the product is also even; otherwise the product is odd; e.g., 4 x 13 = 52). When problems violate both rules, participants use strategy combination and have better performance on both-rule than on one-rule violation problems (i.e., five or parity rule). Aging studies found that older adults efficiently use one-rule violation checking strategies but have difficulties to combine two strategies. To better understand these aging effects, we used EEG and found important age-related changes while participants used rule-violation checking strategies. We compared participants' performance while they verified arithmetic problems that differ in number and type of violated rule. More specifically, both-rule violation problems elicited larger negativity than one-rule violation problems between 600 and 800 ms. Five-rule violation problems differed from parity-rule violation problems between 1100 and 1200 ms. Moreover, rule-violation checking strategies and strategy combination involved delta, theta, and lower alpha frequencies. Age-related changes in ERPs and frequency were associated with less efficient strategy combination. Moreover, efficient use of one-rule violation checking strategies in older adults was associated with changes in ERPs and frequency. These findings contribute to further our understanding of age-related changes and invariance in arithmetic strategies, and in combination of arithmetic strategies.