Subtraction by addition

Abstract

University students' self-reports indicate that they often solve basic subtraction problems (13 - 6 = ?) by reference to the corresponding addition problem (6 + 7 = 13; therefore, 13 - 6 = 7). In this case, solution latency should be faster with subtraction problems presented in addition format (6 + _ = 13) than in standard subtraction format (13 - 6 = _). In Experiment 1, the addition format resembled the standard layout for addition with the sum on the right (6 + _ = 13), whereas in Experiment 2, the addition format resembled subtraction with the minuend on the left (13 = 6 + _). Both experiments demonstrated a latency advantage for large problems (minuend >10) in the addition format as compared with the subtraction format (13 - 6 = _), although the effect was larger in Experiment 1 (254 msec) than in Experiment 2 (125 msec). Small subtractions (minuend ≤10) in Experiment 1 were solved equally quickly in the subtraction or addition format, but in Experiment 2, performance on small problems was faster in the standard format (5 - 3 = _) than in the addition format (5 = 3 + _). The results indicate that educated adults often use addition reference to solve large simple subtraction problems, but that they rely on direct memory retrieval for small subtractions. Copyright 2008 Psychonomic Society, Inc.