Younger and older participants were asked to indicate if 240 complex two-digit addition problems were smaller than 100 or not. Half of the problems were small-split problems (i.e., the proposed sums were 2% or 5% away from 100; e.g., 53 + 49) and half were large-split problems (i.e., proposed sums were 10% or 15% away from 100; 46 + 39). Behavioral and event-related potential (ERP) data revealed that (a) both groups showed a split effect on both reaction times and percent errors, (b) split effects were smaller for older than for younger adults in ERPs, and (c) the hemispheric asymmetry (left hemisphere advantage) reported for younger adults was reduced in older adults (age-related hemispheric asymmetry reduction). These results suggest that older adults tend to use only one strategy to solve all problems, whereas younger adults flexibly and adaptively use different strategies for small- and large-split problems. Implications of these findings for our understanding of age-related similarities and differences in arithmetic problem-solving are discussed.