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Summary tasks have the following implications:

• A summary task’s planned start date, planned finish date and duration are automatically calculated based on its sub tasks and therefore, cannot be entered manually. The start date is the minimum of the start dates of its sub tasks, while the finish date is the maximum of the end dates of its sub tasks.
• The duration is the max elapsed working days between the start and finish dates.
• Constraint dates are not applicable for summary tasks.
• Budget of a summary task is the sum of budgets of all its sub tasks.
• Estimated Planned Cost of a summary task is the sum of estimated Planned costs of all its sub tasks.
• Resources assigned to a summary task will not be factored into the estimated planned cost of the summary task, nor displayed on the RLC
• The % Complete of a summary task is automatically calculated as the weighted sum of percent complete of all its sub tasks and explained as follows :
  
  If p is the percentage complete of a task and w is the estimated planned effort on a task, then:

Percentage complete of a summary task = (w1 x p1 + w2 x p2+...) / (w1 + w2 +...), where 1, 2, 3... are its sub tasks. 

To illustrate it further, let us consider an example :

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In cases where child tasks do not have any resource assignments, their planned effort (work) for purpose of %Complete for its Summary Task is considered assuming a 100% assignment. For example, in T2 above, the effort for purpose of % Complete calculation of Summary Task is assumed to be 16h  (2d task).

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