<p>Increased proficiency when solving arithmetic problems may have two origins. During learning, problems may be associated with their respective outcome and retrieved from memory when probed. Alternatively, acceleration of procedural solving strategies may lead to the observed improvements. The study examined the effects of a four-day drill training on complex addition and subtraction problems at both behavioral and neural levels. Significant improvement in performance was observed, reflected by a decrease in response times and increase in accuracy for specific groups of problems. At the neural level, we observed increased univariate activation in the parieto-occipital regions for problem groups showing the most pronounced training effect. These areas were previously linked to eye-movements and could hence accommodate more proficient visuospatial transformations, leading to an increase in procedural efficiency. Multivariate decoding showed changes in activity patterns in all ROIs between sessions, suggesting automatization of arithmetic strategies. Right hippocampus activation patterns indicated training-induced changes linked to memory retrieval. Representational similarity analysis, however, revealed that training-specific memory effects are not related to increased procedural efficiency alone. On the univariate level, the current data seem to support the acceleration of the procedural solving hypothesis. However, the inconclusiveness of the multivariate analyses and the involvement of the hippocampus indicate parallel use of arithmetic fact retrieval. The study highlights the importance of complementary analysis techniques and demonstrates the context-sensitivity of arithmetic learning by using complex addition and subtraction problems (two-digit addition and subtraction problems).</p>