This work introduces scheduling algorithms to maximize the expected number of independent tasks that can be executed on a parallel platform within a given budget and under a deadline constraint. The main motivation for this problem comes from imprecise computations, where each job has a mandatory part and an optional part, and the objective is to maximize the number of optional parts that are successfully executed, in order to improve the accuracy of the results. The optional parts of the jobs represent the independent tasks of our problem. Task execution times are not known before execution; instead, the only information available to the scheduler is that they obey some (unknown) probability distribution. The scheduler needs to acquire some information before deciding for a cutting threshold: instead of allowing all tasks to run until completion, one may want to interrupt long-running tasks at some point. In addition, the cutting threshold may be reevaluated as new information is acquired when the execution progresses further. This work presents several algorithms to determine a good cutting threshold, and to decide when to re-evaluate it. In particular, we use the Kaplan-Meier estimator to account for tasks that are still running when making a decision. The efficiency of our algorithms is assessed through an extensive set of simulations with various budget and deadline values, and ranging over 13 probability Scheduling Stochastic Tasks With Unknown Probability Distribution distributions. In particular, the AutoPerSurvival(40%,0.005) strategy is proved to have a performance of 77% compared to the upper bound even in the worst case. This shows the robustness of our strategy.