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FM scheduling problem and critical path analysis

7.4 Using Crashing to Reduce Completion Time

Note: if you cannot remember how to determine the critical path of an activity network, revise notes for 7.3 Determine Critical Paths and Float Times.

Crashing

  • Crashing refers to the process of reducing the duration of one or more activity in a project and then recalculating the project duration.
  • Crashing could represent anything that reduces the duration of an activity, such as hiring more staff, favourable weather, utilising more efficient methods, etc.
  • Crashing an activity on the critical path will generally lower the project duration.
  • Crashing an activity which is not on the critical path will not change the project duration.
Read More »7.4 Using Crashing to Reduce Completion Time

7.3 Determine Critical Paths and Float Times

Note: if you cannot remember how to apply forward and backward scanning, revise notes for 7.2 Forward and Backward Scanning.

Float Times

  • The float time for an activity is the difference between its latest start time (LST) and earliest start time (EST).
  • This represents the amount of time the individual activity can be postponed without changing the duration of the project overall.

Example

Picture 5

Above is an activity network which has undergone forward and backward scanning to determine the EST and LST of each activity. The float times of each activity can be calculated from these values:

Read More »7.3 Determine Critical Paths and Float Times

7.2 Forward and Backward Scanning

Note: if you cannot remember how to construct and analyse an activity network, revise notes for 7.1 Activity Networks.

Scheduling Problem

  • It is a problem of determining the minimum completion time for a project given its events.

Earliest Start Time (EST)

  • The earliest possible time that an activity can start.
  • The earliest finishing time of an activity = EST of an activity + Duration of an activity

Forward Scanning

  • Forward scanning is a methodical process for finding the earliest start time (EST) for each activity in an activity diagram. The process works as follows:
Read More »7.2 Forward and Backward Scanning

7.1 Activity Networks

Precedence Tables

  • A precedence table lists each activity required to complete a project and the activities which need to be completed immediately before the activity can be begin. These are arranged into 2 columns.
  • In many cases a third column is added (in the middle), listing the estimated duration of each activity.

Example

Activity

Duration (mins)

Predecessors

Boil water (B)

10

Prepare Sauce (P)

15

Cook Pasta (C)

15

Boil water

Mix Sauce and Pasta (M)

2

Prepare Sauce, Cook Pasta

Activity Networks

Read More »7.1 Activity Networks