A discrete-time approximation technique for the time-cost trade-off in PERT networks Amir Azaron, Masatoshi Sakawa, Reza Tavakkoli-Moghaddam and Nima Safaei RAIRO-Oper. Res., 41 1 (2007) 61-81 Published online: 15 June 2007 DOI: 10.1051/ro:2007005