Akingbade, Toluwalase Janet, and Fabian C. Okafor. “A Class of Ratio-Type Estimator Using Two Auxiliary Variables for Estimating The Population Mean With Some Known Population Parameters”. Pakistan Journal of Statistics and Operation Research 15, no. 2 (June 12, 2019): 329-340. Accessed January 17, 2021. https://pjsor.com/pjsor/article/view/2558.