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Construction Management Study Lab

Time Management

10% of the exam

Time Management is 10% of the exam and centers on the Critical Path Method. You will fill in activity boxes: forward pass for early dates, backward pass for late dates, then total and free float. The exam uses the day-one convention — the first day of an activity is day 1, so EF = ES + Duration − 1 and LS = LF − Duration + 1.

Two merge rules do most of the work. Going forward, when several arrows enter one activity, take the LATER value — an activity waits for its slowest predecessor. Going backward, when one activity feeds several successors, take the EARLIER value. Lags shift the arithmetic by their value (an FS+2 successor starts two days after the predecessor finishes; an SS+5 successor starts five days after the predecessor starts).

Float questions reduce to the 'who gets hurt' test: if using the slack only threatens the project end date, that is total float (LF − EF); if it threatens the next activity's early start, that is free float. Critical path activities have zero total float. Practice until the passes are mechanical — our CPM trainer exists for exactly this.

Key concepts

  • PDM activity box: ES/EF on top, LS/LF below, floats at the bottom
  • Relationships: FS (most common), SS, FF, SF — plus lags and leads
  • Forward pass: EF = ES + D − 1; merge = take later
  • Backward pass: LS = LF − D + 1; merge = take earlier
  • Total Float = LF − EF = LS − ES; Free Float = ES(successor) − EF − 1
  • Crashing (add cost) vs. fast-tracking (add risk)

Exam tips

  • The last activity has no room to be late: its LF equals its EF
  • Free float never exceeds total float
  • Baseline vs. updated schedule distinctions show up in judgment questions — the baseline is the contractual yardstick

Practise the passes interactively

Reading the rules is not the same as running them. The CPM Interactive Trainer walks you through a seven-activity network one field at a time — 42 steps covering the forward pass, the backward pass, and both floats — checking every answer as you type and explaining the merge rules and the classic total-float-versus-free-float trap. Two more networks let you self-test, including one with FS+2, SS+5 and FS−2 lags like the exam uses.

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72 practice questions in this domain

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