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.

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.