[1] Bayero Univ, Sch Continuing Educ, Dept Sci, PMB 3011, Kano, Nigeria
[2] Abubakar Tafawa Balewa Univ, Fac Sci, Dept Math Sci, PMB 0248, Bauchi, Nigeria
[3] Bayero Univ, Fac Phys Sci, Dept Math Sci, Numer Optimizat Res Grp, Kano 700241, Nigeria
[4] Sefako Makgatho Hlth Sci Univ, Dept Math & Appl Math, ZA-0204 Pretoria, South Africa