This is the accepted version of the following article: [Eisenberg, T. (2015), Problems Section. School Science and Mathematics, 115: 427. doi: 10.1111/ssm.12147], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/ssm.12147/abstract
Diaz-Barrero, J.L. [Solution to the problem] 5377[: a metric inequality]. "School science and mathematics [en línia]", Desembre 2015, vol. 115, núm. 8, p. 427.