The 84% Method: A Terminal-Digit Selection Heuristic for Two-Digit Mental Multiplication
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Abstract
The 84% Method is a selection heuristic for two-digit mental multiplication. It classifies a factor as favorable when its units digit is 0, 1, 2, 5, 8, or 9. Under uniformly distributed terminal digits, the probability that at least one of two factors is favorable is 1 − (4/10)² = 84%. The 84% figure refers to the coverage of the selection criterion, not to a measured speed improvement.
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View paper (DOI)Open access versionOpenAlexZenodo (CERN European Organization for Nuclear Research)Published 2026-09-05
Authors: Timon Felice Amand Roder
Institutions: University of Tübingen