Younger and older adults were taught new strategies for converting amounts presented in French francs into euros or amounts presented in euros into French francs. The choice/no-choice method was used to obtain information on how often each newly learned strategy was used as well as information on the speed and accuracy of strategies. The results showed that both younger and older participants used the new conversion strategies unequally often and had strategy preferences that were justified by the relative ease of execution of each strategy. We discuss numerous practical applications of the present findings, as they suggest that one can help younger and older people by teaching them the add-half and divide-three strategies for the French-franc-euro conversions, that no specific strategies should be taught to older people, and that newly taught strategies are more efficient than those people use spontaneously.