[zcanann]

I always think of project tasks as flow charts, where every item either takes 1 day, or 1 week. There's no way of really knowing in advance. Complications happen.

It makes it really hard to calculate the "expected value" of 5-10 tasks.

[dTal]

The more tasks you have to do, the more certain about duration you should be - some of the uncertainty will cancel out and you will get a gaussian distribution. For your example, I expect 10 tasks of between 1 day and 1 week each (with flat probability) to take about 6 weeks in total, with a 95% chance of completion within 7 weeks.