I Syed is using probability distribution to determine the time to use for a particular activity on his project. He estimates that if he puts his best workers on the task that they will finish in 8 days. If he put his least experienced workers on the task they will finish in 20 days but if he has a mix of worker most likely they will be done in 11 days. What level of 0' (sigma) should he use to estimate that the task will take between 8 and 16 days