Simple interest is not so simple

Arturo Lorenzo Valdés


Simple interest and solving problems involving it by value equations are presented incorrectly in different textbooks, since in these it is affirmed that the solution depends on the focal date used. This paper develops and illustrates the correct way to solve problems involving simple interest. The accumulation function and amount function under simple and compound interest are presented. It is explained and illustrated the proper use of the amount function under simple interest in expressing and solving the equation of value at different focal dates. It is shown that solving equations of value involving simple interest, should give the same result regardless of the focal date.


Simple interest, value equation, focal date

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CABEZA, L. (2010). “Cavilaciones sobre el interés simple,” Zona Próxima. (12), 158-175.

KELLISON, S. G. (2009). The theory of interest, Third edition., Boston:McGraw-Hill Irwin.

VAALER, L. F., AND DANIEL, J. W. (2008). Mathematical Interest Theory, Second edition., Washington, DC: Mathematical Association of America.


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