formula for free float calculation

Submitted by y0zh on Sat, 05/25/2013 - 18:20

 do we use LS - ES of successor? because I found this one formula and got confused:

Free float=ES of the following activity-ES of the present activity-duration of the present activity

http://www.scribd.com/doc/28680971/101-PMP-Sample-Questions-for-the-PMP-Exam

Question 38 and my answer is Task Two free float=7 which is not presented there. Please clarify

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Fariba

Sat, 05/25/2013 - 21:31

I am going through the same questions and it really confused me.

appreciate any help.

Having problem with Question 44 as well. I selected B but the answer is C.
http://www.scribd.com/doc/28680971/101-PMP-Sample-Questions-for-the-PMP-...

vijayavadrevu

Sun, 05/26/2013 - 10:24

 For question 44,

if you observe task 6 is on critical path, float given as 0.

Float = LF-EF or LS-ES

LF and EF are given as 15 & 15.

LS is given as 6.

So ES = LS-Float = 6-0 =6

This is how I have solved the problem. 

May be someone can clarify whether this is right approach or not?

vijayavadrevu

Sun, 05/26/2013 - 10:55

 For question 38, the options are referring to free float.

Please refer to the following link where the difference between free float and total float is given. The formula LS-ES , you are referring to, is for the total float

http://pmi.books24x7.com/assetviewer.aspx?bookid=45514&chunkid=397723927

With this, option 2 i.e., task 2 having free float of 6 days is correct.

y0zh

Sun, 05/26/2013 - 13:09

Can you provide your variant of formula? EF of predecessor - ES of succesor= free float

vijayavadrevu

Sun, 05/26/2013 - 15:56

 Have gone through question 38 referred by you. Could not paste the image

With my little bit of understanding I am providing the 2 solutions. I may be right or wrong in my approach  which may have to be confirmed by some experts of this forum. Iam just a learner

Regards

Vijaya

 

Solution 1:

 

Please refer to

 

http://pmi.books24x7.com/assetviewer.aspx?bookid=41937&chunkid=922918066&noteMenuToggle=0&hitSectionMenuToggle=0&leftMenuState=1

 

For activity  1,

Free Float = Earliest of [ES of successor 2 or ES of successor 3] – EF of activity 1 – 1 day

 = 7-6-1=0                             option A  i.e., 3 days is wrong

 

For activity 2,

Free Float = ES of activity 4 – EF of activity 2 – 1

= 17-10-1=6                         option B  i.e., 6 days is correct

 

For activity 3,

Free Float = ES of activity 4 – EF of activity 3 – 1

=17-16-1 = 0                        option C  i.e., 9 days is wrong

 

For activity 4,

Free Float = ES of activity ?? (not given) – EF of activity 4 – 1

Cannot be determined.      Option 4 i.e., 5 days is wrong

 

Solution 2:

 

Please refer to

 

 

http://pmi.books24x7.com/assetviewer.aspx?bookid=45514&chunkid=397723927

 

Free Float = Earliest ES of Following Activities - ES of Present Activity - Duration of Present Activity

 

For activity 1,

Free Float = Earliest of [ES of successor 2 or ES of successor 3] - ES of activity 1 - Duration of activity 1

 = 7-1-6=0                             option A is wrong

 

For activity 2,

Free Float = ES of activity 4 – ES of activity 2 – Duration of activity 2

= 17-7-4=6                            option B is correct

 

For activity 3,

Free Float = ES of activity 4 – ES of activity 3 – Duration of activity 3

=17- 7-10 = 0                       option C  is wrong

 

For activity 4,

Free Float = ES of activity ?? (not given) – EF of activity 4 – 1

Cannot be determined.      Option 4 is wrong

 

 

Also we have the formula

 

EF of Activity 1 = ES of Activity 1 + ED of Activity 1 - 1 day

 

For task 2,

Free Float     = ES of activity 4 – EF of activity 2 – 1

= ES of activity 4 – [ES of Activity 2 + ED of Activity 2 - 1 day] -1

=17-[7+4-1]-1

= 17-10-1

= 6

y0zh

Sun, 05/26/2013 - 17:41

Question to experts. In the formula above there is -1. Does this mean that we are reffering to the network diagram with 1 day not 0 day start. Sorry, noting from ipad, not able to paste a reference