GATE IT 2004 | Question: 68

Question

A software project involves execution of 5 tasks T1, T2, T3, T4 and T5 of duration 10, 15, 18, 30 and 40 days, respectively. T2 and T4 can start only after T1 completes. T3 can start after T2 completes. T5 can start only after both T3 and T4 complete. What is the slack time of the task T3 in days?

• A. 0
• B. 3
• C. 18
• D. 30

Answer 1

Slack time can be defined as the amount of time an task can be delayed without causing another task to be delayed or impacting the completion date of your project.

There are two things that are needed to calculate the slack time:

1. ES – the earliest time when an activity can be started
2. LS – the latest time when an activity must be started.

The slack time is calculated as:

Slack Time = LS-ES

ES of T3 is after completion of T1 and T2 so

ES=T1+T2=10+15=25

T5: ES =10+15+18=43

T3: LS =43-18=25
Slack time = ES-LS =25-25=0 // For T3

Comments

and slack time of T4 is 3 days

Answer 2

T3 : earliest start time - after T2 and T1 completes , i.e (10+15) = 25

       T5 can start earliest by 43

       so latest start time of T3 (43-18)= 25

      hence, slack time = 25-25=0

ans. 1.