We examined whether older adults use plausibility-checking strategies while verifying arithmetic problems. We also tested trial-to-trial modulations of plausibility-checking strategies, and aging effects on these sequential modulations. We asked young and older adults to verify arithmetic problems that violated or respected arithmetic rules (i.e., 5x16 = 87. True/False?). Both young and older adults solved problems violating parity rule and five rule more quickly than problems violating no rule. We also found that both age groups had better performance when both five rule and parity rule are violated than when only one or no rules are violated. These results suggest age invariance in using rule-violation checking strategies and a smaller, but still efficient, strategy combination in older adults. Finally, for young adults only, strategy combination was larger following problems violating rules than after problems respecting rules. These findings have important implications regarding mechanisms underlying age-related differences in using rule-violation checking strategies to verify arithmetic problems and in combining two strategies into a single, more efficient one.