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The presentation is part of Ace the PMP Exam, available on the iBookstore. Go to http://Aceitguides.com for more information. The critical path is the longest path in a network diagram, and therefore determines the shortest time that it will take to complete a project. This systematic way of determining the critical path uses the techniques of forward pass and backward pass. For a simple way of determining the critical path, useful for quickly answering some questions on the PMP® exam, see A Simple Method of Determining the Critical Path video in this series.
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The Critical Path
Method
This presentation is part ofAce the PMP Exam
A systematic method for determining the critical path
The critical path is the longest path in a network diagram, and therefore determines the shortest time that it will take to complete a project.
This systematic way of determining the critical path uses the techniques of forward pass and backward pass.
A systematic method for determining the critical path
You use a forward pass to calculate the Early Start and Early Finish times and a backward pass to calculate the Late Start and Late Finish times, and therefore calculate the float. Let’s look at what these mean.
•Early Start — the earliest time that the activity can logically start
•Early Finish — the earliest time that the activity can logically finish
•Late Start — the latest time the activity can logically start without delaying the project or a milestone
•Late Finish — the latest time the activity can logically finish without delaying the project or a milestone
•Float — the amount of time an activity can be delayed without affecting the project schedule
The Forward Pass
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The Forward Pass
We will use the forward pass to determine the Early Start and Early Finish values of all the activities.
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The Early Finish is The Early Finish is the Early Start plus the Early Start plus the duration of the the duration of the
activityactivity
The Early Start is the The Early Start is the value from the value from the StartStart
MilestoneMilestone
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We will use the forward pass to determine the Early Start and Early Finish values of all the activities.
Activity A
Activity A
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The Early Finish is The Early Finish is the Early Start plus the Early Start plus the duration of the the duration of the
activityactivity
The Early Start is The Early Start is the value from the value from
the the StartStart MilestoneMilestone
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The Early Finish is The Early Finish is the Early Start plus the Early Start plus the duration of the the duration of the
activityactivity
The Early Start is the The Early Start is the value from the value from the StartStart
MilestoneMilestone
Activity B
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StartStart EndEndThe Early Start is The Early Start is the value from the value from
the the StartStart MilestoneMilestone
The Early Finish is The Early Finish is the Early Start plus the Early Start plus the duration of the the duration of the
activityactivity
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The Early Finish is The Early Finish is the Early Start plus the Early Start plus the duration of the the duration of the
activityactivity
The Early Start is The Early Start is the value from the value from
the the StartStart MilestoneMilestone
Activity C
Activity B
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StartStart EndEnd
The Early Finish is The Early Finish is the Early Start plus the Early Start plus the duration of the the duration of the
activityactivity
The Early Start is The Early Start is the Early Finish the Early Finish
value from value from Activity AActivity A
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The Early Start is The Early Start is the value from the value from
the the StartStart MilestoneMilestone
The Early Finish is The Early Finish is the Early Start plus the Early Start plus the duration of the the duration of the
activityactivity
Activity D
Activity C
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The Early Finish is the The Early Finish is the Early Start plus the Early Start plus the
duration of the activityduration of the activity
The Early Start is The Early Start is the Early Finish the Early Finish
value from value from Activity Activity B B (not (not Activity CActivity C) ) as this is the later as this is the later Early Finish time.Early Finish time.
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The Early Finish is The Early Finish is the Early Start plus the Early Start plus the duration of the the duration of the
activityactivity
The Early Start is The Early Start is the Early Finish the Early Finish
value from value from Activity AActivity A
Activity DActivity E
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8 11
B8B8
0 8
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0 4
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8 10StartStart EndEnd
The Early Finish is the The Early Finish is the Early Start plus the Early Start plus the
duration of the activityduration of the activity
The Early Start is the Early The Early Start is the Early Finish value from Finish value from Activity B Activity B (not (not Activity DActivity D) as this is the ) as this is the
later Early Finish time.later Early Finish time.
The Early Finish is the The Early Finish is the Early Start plus the Early Start plus the
duration of the activityduration of the activity
The Early Start is The Early Start is the Early Finish the Early Finish
value from value from Activity Activity B B (not (not Activity CActivity C) ) as this is the later as this is the later Early Finish time.Early Finish time.
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Activity E
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Activity F
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End MilestoneActivity F
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The Early Finish is the The Early Finish is the Early Start plus the Early Start plus the
duration of the activityduration of the activity
The Early Start is the Early The Early Start is the Early Finish value from Finish value from Activity B Activity B (not (not Activity DActivity D) as this is the ) as this is the
later Early Finish time.later Early Finish time.
The value for the The value for the End End milestone is the milestone is the Early Finish value from Early Finish value from Activity F Activity F (not (not
Activity EActivity E) as this is the later Early ) as this is the later Early Finish time.Finish time.
✓
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That completes the forward pass
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End Milestone
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The value for the The value for the End End milestone is the milestone is the Early Finish value from Early Finish value from Activity F Activity F (not (not
Activity EActivity E) as this is the later Early ) as this is the later Early Finish time.Finish time.
The Backward Pass
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We will use the backward pass to determine the Late Start and Late Finish values of all the activities.
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The Backward Pass
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The Late Start is the Late The Late Start is the Late Finish minus the duration of Finish minus the duration of
the activitythe activity
The Late Finish is the The Late Finish is the value from the value from the EndEnd
MilestoneMilestone
We will use the backward pass to determine the Late Start and Late Finish values of all the activities.
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Activity F
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StartStart EndEndThe Late Start is the The Late Start is the Late Finish minus the Late Finish minus the
duration of the activityduration of the activity
The Late Finish The Late Finish is the value is the value
from the from the EndEnd MilestoneMilestone
The Late Start is the Late The Late Start is the Late Finish minus the duration of Finish minus the duration of
the activitythe activity
The Late Finish is the The Late Finish is the value from the value from the EndEnd
MilestoneMilestone
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Activity EActivity F
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StartStart EndEnd
The Late Start is the Late The Late Start is the Late Finish minus the duration of Finish minus the duration of
the activitythe activity
The Late Finish is the The Late Finish is the Late Start value from Late Start value from
Activity FActivity F
The Late Start is the The Late Start is the Late Finish minus the Late Finish minus the
duration of the activityduration of the activity
The Late Finish The Late Finish is the value is the value
from the from the EndEnd MilestoneMilestone
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Activity DActivity E
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StartStart EndEndThe Late Start is The Late Start is the Late Finish the Late Finish
minus the minus the duration of the duration of the
activityactivity
The Late Finish is the The Late Finish is the Late Start value from Late Start value from
Activity EActivity E
The Late Start is the Late The Late Start is the Late Finish minus the duration of Finish minus the duration of
the activitythe activity
The Late Finish is the The Late Finish is the Late Start value from Late Start value from
Activity FActivity F
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Activity CActivity D
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StartStart EndEnd
The Late Start is the The Late Start is the Late Finish minus Late Finish minus the duration of the the duration of the
activityactivity The Late Finish is the Late Start The Late Finish is the Late Start value from value from Activity F Activity F (not (not
Activity EActivity E) as this is the earlier ) as this is the earlier Late Start time.Late Start time.
The Late Start is The Late Start is the Late Finish the Late Finish
minus the minus the duration of the duration of the
activityactivity
The Late Finish is the The Late Finish is the Late Start value from Late Start value from
Activity EActivity E
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Activity B
Activity C
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Activity B
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StartStart EndEnd
The Late Start is the The Late Start is the Late Finish minus Late Finish minus the duration of the the duration of the
activityactivity
The Late Finish is The Late Finish is the Late Start the Late Start
value from value from Activity DActivity D
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Activity A
The Late Start is the The Late Start is the Late Finish minus Late Finish minus the duration of the the duration of the
activityactivity The Late Finish is the Late Start The Late Finish is the Late Start value from value from Activity F Activity F (not (not
Activity EActivity E) as this is the earlier ) as this is the earlier Late Start time.Late Start time.
✓
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That completes the backward pass
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Activity A
The Late Start is the The Late Start is the Late Finish minus Late Finish minus the duration of the the duration of the
activityactivity
The Late Finish is The Late Finish is the Late Start the Late Start
value from value from Activity DActivity D
If an activity can be delayed it is said to have float (or slack). To calculate float you subtract the Early Start from the Late Start (or the Early Finish from the Late Finish, it amounts to the same thing).
The amount of float is indicated as a number above the box.
Calculating float
Here is the network diagram with the float indicated above each activity
Calculating float
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The critical path is the path through the activities that have no float, in this case activities B and F.
The Critical Path
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A systematic method for determining the critical path
That was a systematic method of determining the critical path in a network diagram using the forward pass and the backward pass.
For a simple way of determining the critical path, useful for quickly answering some questions on the PMP® exam, see A Simple Method of Determining the Critical Path video in this series.
The Critical Path
Method
This presentation is part ofAce the PMP Exam
