Teaching Arithmetic
Sir, —ln “Why Tommy Can’t Do Sums,” your contributor says: “Arithmetic is an exact subject. An answer is either right or wrong,” and I have
no doubt that this is so. 3ut can Mr Pringle explain something I have never been able to understand, that if +8 and —7 are added arithmetically the answer is 15 but if they are added algebraically the answer is +l?—Yours, etc., TREVOR W. STRINGER. March 7, 1968. [Mr D. J. C. Pringle comments: “1 can only say that such an arithmetical practice constitutes one of the difficulties I encounter at present in endeavouring to teach subtractions of mixed numbers. Someone with a kink for twisting arithmetical concepts could conceivably say, ‘ln Vietnam an American platoon lost 7 men killed ( —7), and received 8 men as reinforcements (18); therefore 15 separate bodies were involved. However, the net gain in platoon strength was 1 man, and the platoon would jolly well know that for a fact, arithmetic, algebraic, commissariat or logistic’.”)
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Bibliographic details
Press, Volume CVIII, Issue 31631, 18 March 1968, Page 12
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167Teaching Arithmetic Press, Volume CVIII, Issue 31631, 18 March 1968, Page 12
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