Maree, J., J. Molepo, J. Owen, and R. Ehlers. “Problem-Based Approach to Mathematics in Grades 9 and 11 in the Limpopo Province”. Suid-Afrikaans Tydskrif Vir Natuurwetenskap En Tegnologie / <i>South African Journal of Science and Technology</I&gt;, Vol. 24, no. 4, Sept. 2005, pp. 124-33, doi:10.4102/satnt.v24i4.181.