Efficiency and flexibility of indirect addition in the domain of multi-digit subtraction

This article discusses the characteristics of the indirect addition strategy (IA) in the domain of multi-digit subtraction. In two studies, adults' use of IA on three-digit subtractions with a small, medium, or large difference between the integers was analysed using the choice/no-choice method. Results from both studies indicate that adults spontaneously apply IA on three-digit subtractions, and use IA with the same frequency as direct subtraction (DS) strategies. Furthermore, IA resulted in faster responses – without any loss in accuracy – than DS. Finally, adults flexibly applied IA and DS strategies on the basis of task and individual strategy performance characteristics. Our results support theoretical models on adaptive strategy choices, and question instructional practices focusing on the routine mastery of only DS.