Duration calculation

Hello friends,

 This question is also from oliverlehmanns 75 questions. This is regarding 32nd question, when I calculated the duration is coming as 39 days where as the answer shows 37 days.

 I have taken FF-2 days as lead of 2 days and FS+3days as lag of 3 days. So I calculated the durations as  20(activity1)+10(activity2)+5-2(activity 3 has two days lead) + 6+3(as the activity 4 has 3 days lag)  which comes to 39 days.

am I doing anythig wrong in calculation.


appreciate your help  


Thanks in advance


Oliver questions are not that easy uh? But it's a good chance to improve skills.


I took a look and I guess you're talking about the previous question (31st) , right?


Activity 3 finishes 2 days BEFORE activity 2 (it's a finish-to-finish relationship). As activity 2 has 10 days, activity 3 is not included in the critical path (it's kind of swallowed by activity 2).

 THUS, activity 4 starts 2 days before activity 2 finishes.

Activity 1: 20 days

Activity 2: 10 days

Activity 4: 6 days + 3 days (lag) - 2 days (due activity 3 constraint)

37 days.




Thank you for the update. but here when you say Finish to Finish relation ship between activity 2 to activity 3..

 as per my understanding, activity 3 will not be finished until activity 2 finishes. so as per this, first activity 2 will be finished which is 10 days. next activity 3 will be finished.

I am still not convinced with the explanation. could you please clarify where I m wrong?



It's the opposite.

 Activity 3 must finish 2 days before activity 2 finishes (FF - 2). The minus sign indicates that sucessor activity is going to finish first (it's a lead). If you had a plus (+) sign, the activity is going to finish after (it's a lag). If nothing is said, both activity will finish the same time.

I guess you're confusing leads and lags because it's a Finish to Finish. You must add or take them from the FINISH of sucessor activity.

If you're talking about Finish to Start, you add or take them from the START of the sucessor activity. 

 Better now or still in doubt?


Hi Robis

 Thanks a lot. Now I am clear about FF relationship.

 Thank you very much for the detailed explanation.