Hi

Anybody, please point me to some book/notes for the calulation of PERT. I know it is easy for some people

but I reeally need to understand how to calulate these PERT related questions easily and fast.

For example, In the following quesiton, the answer is 50%. How you calculate this? Do you need to perform

some calulations or you just use Normal Distribution 'bell-shaped' curve? I just dont understand this