The optimistic, most likely and pessimistic time estimates of an activity are 5, 10 and 21 days respectively. What are the expected time and standard deviation respectively ?

Consider the following statements : The use of relatively weak motor 1. will accommodate movements due to loads, cracking if any and will be distributed as thin hair cracks which are less noticeable or harmful. 2. will result in reduction of stresses due to differential expansion of masonry units. Of these statements :

A stone dropped from the top of a tower is found to travel (5/9) of the height of the tower during the last second of its fall. What is the total time of fall ?