In this paper, the balancing problem of assembly lines with skilled and unskilled workers while there the
possibility of installing multi-manned workstations is addressed. In such a system, the skilled workers are hired
permanently while the unskilled ones can be hired temporarily in order to meet the seasonal demands. A mixed
integer programming formulation is presented to solve this problem. The objective is to minimize the number of
temporary workers as the first objective and the number of workstations as the second one. The proposed
formulation has been used to solve some experimental instance found in the literature. The results validate the
effectiveness of installing multi-manned workstations in comparison to single-manned ones proposed in literature.