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ERIC Number: EJ859714
Record Type: Journal
Publication Date: 2009-Jan
Pages: 2
Abstractor: ERIC
Reference Count: 0
ISSN: ISSN-0025-5785
Explaining the Cross-Multiplication Algorithm
Handa, Yuichi
Mathematics Teaching, n212 p8-9 Jan 2009
Many high-school mathematics teachers have likely been asked by a student, "Why does the cross-multiplication algorithm work?" It is a commonly used algorithm when dealing with proportion problems, conversion of units, or fractional linear equations. For most teachers, the explanation usually involves the idea of finding a common denominator--one in particular. One might even draw arrows in the first equation, showing how the "a" and the "d" come together, and so on. In this article, the author offers a surprising visual "proof" for the algorithm in a manner that is appropriate for a high-school mathematics classroom. The author also explores some important mathematical ideas appropriate for high-school students, especially if they have been exploring the topic of similarity among geometric figures. (Contains 5 figures.)
Association of Teachers of Mathematics. Unit 7 Prime Industrial Park, Shaftesbury Street, Derby, DE23 8YB, UK. Tel: +44-1332-346599; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Descriptive
Education Level: High Schools
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A