float question

Submitted by sunitaPMP on Sat, 03/09/2013 - 19:52

Pls help with this question.This question is already discussed in the forum but am not able to follow those answers.

Q:Activity A has a finish - to-finish relationship with activity B. Activity A has a duration of 10 days. activity B has a duration of 9 days with a 3 day lag. what is the total duration of activty a and B?

1.7 days
2.8 days
3.12 days
4. 9 days


 

Forums: 
PMP / CAPM exam Question bank
  • Log in to post comments
  • 3231 reads

AP

Sat, 03/09/2013 - 21:03

As far as I know, the answer should be 13 days as the relationship given is FF+3.

Activity A will finish on day 10 and since there is a lag of 3 days for Activity B to finish, the total duration should be 13 days.

But if anybody feel I'm totaly out of page, please help me.

 

Regards,

Arun.

sgadewar

Sat, 03/09/2013 - 21:16

Read this it will help you

 

http://www.deepfriedbrainproject.com/2010/01/critical-path-finish-to-fin...

 

The answer is 12, if you carefully understand the example given by cake and heating the owen 

AP

Sat, 03/09/2013 - 21:19

Dear Sameer,

I already went through the discussion in Deep fried brain and  understood what they are trying to tell. But could you please explain us how you got the answer as 12?

 

Regards,

Arun.

sgadewar

Sat, 03/09/2013 - 23:49

Arun

 

Key to F-F relation is that there should be lag between 2 activties and does not matter when they start and they can satrt concurrently. So in this example assuming activity A and then Activity B starts with a lag of 3 days. So I start from day 0 Activity A and activity B after 3 days. However I also know activity B takes 9 days and I am sure at this point which is at end of day 3 Activity A is going to finish on  before activity B. So all I need now is how much time is required for activity B. So in this case it takes 9 days so all together 9+3= 12. I see your logic of 13 but only problem over there is that you are assuming maximum duration of both the activity and then adding delay to same which is incorrect. 

bkthakkar

Sun, 03/10/2013 - 00:36

FF relationship means, these activities will have to be completed before any subsequent new activity starts which has dependency on these two activities.

Therefore, the answer is 12 as activity B has 3 days as Lag.

Tell me, friends, if i am out of page in this context

 

sspawar

Sun, 03/10/2013 - 02:37

 correct answer would be 13 days.

FF+3

In above case

Bigger one DURation +LAG 

Total dur of A and B activities = 10+3

 

sunitaPMP

Sun, 03/10/2013 - 02:45

Hello Pawar Jee,

So is it always greater Duration +/-  lag(lead)? I mean is it always depends on the activity with greater duration?

 

sspawar

Sun, 03/10/2013 - 03:22

 In this case 

suppose project starts by 6th of March 

we will demonstrate it

 

 


 

by Zero start method like this

  

9

18

    
 

B/9

< 

  
 

 

  
   

 

FF+3

(Start of project by 6th March) 5

15

 

  
 

A/10

 

  
 

> 

  

 

Project is finishing on 18.

thus 6th March morning to 18th March evening = 18-5 = 13 days

 

sgadewar

Sun, 03/10/2013 - 12:07

If project starts on 6th March then it should be represented by 6 [6th Morning] in above diagram however it shown as 5. I doubt if this would be correct. We need to substitue 6 rather than 5. Also with FF+3 the start date for B would be 5+3= 8 and not 9. Because it would work this way, March 5, 6 and 7 , activity B will wait as it needs to wait entire 3 days long. So by that logic by waiting on those days activity B can only start on March 8th and not march 9th.

Could we try to calculate above problem assuming project start date is March 1st?  

 

I still feel answer is 12 and not 13

 

Sameer

AP

Sun, 03/10/2013 - 12:32

Dear Sameer,

I think the problem is that the lag is applied incorrectly. You are considering the relationship as SS+3 instead of FF+3. We need not worry about the start date when the relationship is FF.

Also since Pawar is using ZERO start method, the ES of activity A will be mentioned as 5 only rather than 6. But whatever method (ZERO or ONE start) is used, the Avtivity A will finish on 15th. 

Avctivity B can finish only 3 days after activity A finishes which makes the EF of activity B as 18th. Hence the duration will be 13 days.

Ok, lets calculate using March 1st as the start date for activity A.

Activity A will start on 01-Mar and end on 10-Mar. Since there is a FF relationship, we need to calculate EF of activity B which will be EFof Activity A + 3 days (FF+3, activity B can finish only 3 days after activity A finishes). Hence EF of activity B will be 13.

Please correct me if I'm wrong.

 

Regards,

Arun.

sgadewar

Sun, 03/10/2013 - 12:40

 Arun yes you are correct I was using SS and not FF. but again if I go by March 1st as date EF of activity B is 13. And ES of activity A is March 1st. hence total duration would be 13 - 1 = 12. Am I wrong still? or May be I am confused now or still need more clarity

AP

Sun, 03/10/2013 - 12:47

Dear Sameer,

If you are going by 01-Mar as the ES for activity A, then you are using 1 start method. In this method, the duration can be calculated as EF of activity B - ES of activity A + 1.

Now going by simple maths without any formula, start counting by hand from 01-Mar (morning) to 13-Mar (evening). The duration will be 13 days.

Hope this helps.

 

Regards,

Arun.

sgadewar

Sun, 03/10/2013 - 12:45

 Also arun if I caluclate on finger the actual days it would be March 5, 6,7,8,9,10,11,12,13,14,. So If I actually use the dates the activity A should then finish on end of day 14. If I say 15th then I am taking 11 days right?

AP

Sun, 03/10/2013 - 12:56

Dear Sameer,

In zero start method, the ES of the 1st activity will always be 0 instead of 1 (which is in 1 start method). So, if you are calculating the number of days by finger in zero start method, you need to start calculating from 1 and not 0 (even though 0 is mentioned as ES) as 0 does not make any sense while calculating. 

In the example given by Pawar, even though the ES is mentioned as 5, you need to consider the start as 6 when you calculate by fingers. So, it will be 6th to 15th for 10 day duration.

Hope its clear. Else, please let me know.

 

Regards,

Arun.

sgadewar

Sun, 03/10/2013 - 13:04

 Thanks It is clear Arun 

sspawar

Sun, 03/10/2013 - 02:52

 What is total duration of A and B activities?


B/11

< 

  

 

  
 

 

FF-2
 

 

  

A/10

 

  

> 

  

 

sandeepdel

Sun, 03/10/2013 - 02:58

11 . As need to wait for A to finish. 

sunitaPMP

Sun, 03/10/2013 - 02:59

11 days

sunitaPMP

Sun, 03/10/2013 - 03:26

Pawar Jee,

can you pls explain ans for this?

Seems I am more confused now:)

sandeepdel

Sun, 03/10/2013 - 02:52

 A and B have mandatory relation ff+3. So if I start my activity a on march 2 it will go up to 11 march(total days are 10). Now I need to place a start date for b.. I know that latest date I have to wait up 11 march so what I can do best is that start b on march 2 so that this activity get over by 10 and I used 1 day lag too which is march 11(lag for me here is burden as I am trying to finish my activities as earliest). Now when I reach on march 11, I already completed a and b , and also used 1 day of lag. So now only I have to consider 2 days of lag. I.e march 12 and 13 .So total days from 2 to 13 is 12 days. 

sunitaPMP

Sun, 03/10/2013 - 02:57

I did not understand what you  trying to explain.

sspawar

Sun, 03/10/2013 - 03:46

 In second (my ) question

Suppose project finishes on 15th March.

by question - activity A will finish 2 days later than B. bks activity B is taking 2days lead.

By zero start method we can illustrate it like this:



Here activity B has to start 1st

        
       

2

13

    
 

B/11

< 

  
   

 

  
     

 

FF-2
 

5

15

 

  
   

A/10

 

  
   

> 

  

By this presentation it is clear that project has to be started by activity B on 3rd of March to get finish on March15th .

Thus duration of project will be  = 3rd to 15th = 15-2 = 13 days.

sspawar

Sun, 03/10/2013 - 03:54

 What is total duration of below activities:


B/11

> 

  

 

  
 

 

FF-2
 

 

  

A/10

 

  

< 

  

sunitaPMP

Sun, 03/10/2013 - 04:03

12 days?

sspawar

Sun, 03/10/2013 - 05:58

 Good ,

I think  there is no confusion now.

sunitaPMP

Sun, 03/10/2013 - 06:13

Thanks a lot PawarJi.This really helps:)

Fatemaalhajri

Wed, 03/13/2013 - 06:04

 i diss agree ( please correct me if im mistaken ) 

 

1st we need to understand what does FF means ?

 

Finish-to-Finish (FF) – This relationship is utilized when the completion of two activities should be linked together.

The two activities may start at different times (again, depending on the duration of each activity), but the completion of the two activities is coordinated.

so , 

Activity A has a duration of 10 days.

Activity B has a duration of 9 days with a 3 day lag.

 

they Must finish @ the same time BUT B has a Lag of 3 days so 

lets assume 0 Day is the starting day 

A: will finish after 10 days 

B: will finish after 12 days 

BUT its FF relashinship so, the 

total duration of activty a and B = 12  Days 

 

correct answer is No.3

AP

Wed, 03/13/2013 - 09:22

The definition for FF relationship as per PMBOK is,
Finish-to-finish (FF) - The completion of the successor activity depends upon the completion of the predecessor activity.


Activity B has a duration of 9 days but the lag of 3 days will start only after the completion of activity A. You cannot start the lag after the completion of activity B.


Hence total duration will be 10 + 3 = 13 days.


 


Regards,


Arun.

bkthakkar

Wed, 03/13/2013 - 10:37

Dear Arun and Pawar


Despite the above explanation, reasons are not convincing as I feel we are not reading between the lines of the definition


Def: as mentioned above,


Completion of successor action depends on the completion of predecesor activty


The above definition clearly emphasis, the start date of any activity is not at all a binding cretiria. But the finish date of these two activities are to complete for the next activity to commence in that project


for the problem, A - Predecessor actity - duration 10 days


B- Successor activity - duration 9 days,


In the above case, successor activity is having a 3 days lag and therefore undoubtedly it is going to take 12 days. But since predecesor activity has 10 days which is less than 12 days and therefore it can start 2 days late


Hence i again reiterate, answer is 12 but not 13 as being explained.


Look forward to either clarify me on the above lines if I am wrong .


Regards


Bhavesh Thakkar


 

AP

Wed, 03/13/2013 - 10:49

Dear Bhavesh,


Both our explanation are same except one point.


"In the above case, successor activity is having a 3 days lag and therefore undoubtedly it is going to take 12 days." - Here you have applied the lag after the duration of activity B, i.e., 9 days.


But when there is a FF relationship, even the application of lag will depend on the completion of the predecessor activity. Hence I think the lag of 3 days can start only after Activity A completes, i.e., after day 10.


Kindly let me know If I'm out of page.


 


Regards,


Arun.

bkthakkar

Wed, 03/13/2013 - 15:23

I feel, the error is on the end date.

In FF relationship, end date is firm which should coincide with the both the activities like FS relation, where first activity finishes and then second and similarly SS where two activities will commence at the same time unless some lead or lag isapplied.

On the similar lines, end date of the two activities(here Act A and Act B) will on same day. Since, it has given the 3 day lag of Act B, it will be 9 +3 = 12 days.

hence 12 is the answer.

Hope my understanding of network diagram is correct.

If other colleagues differ they can contribute to answer this question and give its logical end which has been doing lot of rounds till now.

Regards

Bhavesh

.

pmpnewster

Wed, 03/13/2013 - 16:36

Okay... allow me to jump in with my interpretation. Please feel free to differ or correct me as required.

Let's first see if we all agree on how the given lag is applied.

FACT (given in question): Activities are A(10 days) and B(9 days) (in that order) with FF relationship. Lag is given to be 3 days.

FF relationship means that Activity B can finish only AFTER Activity A has finished.

** Now apply the lag: Lag of 3 days means that Activity B finishes 3 days AFTER Activity A has finished. **

Do you agree with the above statements? If no, then this is exactly where the confusion lies and maybe someone else can help us get this clarified. (I am not an expert!)

 

If you do agree with my above explanation, then:  Activity A finishes at the END of Day 10, and hence Activity B has to finish at the END of Day 13 (= 10 + 3 day lag). Duration = 13 days.

Note that I am not concerned with when these activities start, though that info can be deduced.

 

 

 

 

 

 

AP

Wed, 03/13/2013 - 16:38

I totally agree and this is how I have been solving these type of questions and this is how I came to conclusion that the answer is 13 days. We should apply lag only after activity A finishes i.e., 10 days.


Kindly correct us, if you feel we are wrong. I have my exam in 2 days and this will clear my thoughts.


 


Regards,


Arun.

ashshe24

Wed, 03/13/2013 - 17:02

 Activity A has begin And after end of 3rd day  Activity B  Begins (which takes 9days ) so Activity A cannot close until Activity B closes , so its 9+3 =12 Days , On 12th day both A&B close ( F-F) .

AP

Wed, 03/13/2013 - 17:15

Hi,


"Activity A has begin And after end of 3rd day  Activity B  Begins" - You have applied Start-Start relationship. We need not worry about the start of an activity when the relationship is FF.

ashshe24

Wed, 03/13/2013 - 19:18

 I think its F-F , because it shouldnt mater when u start , but it should Finish at same time.

AP

Wed, 03/13/2013 - 19:45

 Lets split the question.

1. Consider the relationship is just FF and no lag is applied. When do you think both the activites will complete?

I think it should complete in 10 days.

 

2. Now consider lag of 3 days. Where do you think this lag should be applied. Is it after the completion of Activity A or B?

I think the lag should be applied after the completion of activity A since activity B can finish only after activity A's completion. Hence the 3 days of lag will start on day 11 and end on day 13. The lag can't start on day 10 as activity A is yet to complete.

 

Hope this makes sense.

ashshe24

Thu, 03/14/2013 - 04:12

13 option itself is no there ??? so hope it makes sense

I rest my case , thanks 

 

mar-rih's picture

mar-rih

Mon, 12/08/2014 - 10:54

I think 12 is correct answer:

 

A: 1 2 3 4 5 6 7 8 9 10   -  -
B:  - - -  1 2 3 4 5 6  7   8  9
D: 1 2 3 4 5 6 7 8 9 19 11 12

 

ggopi111

Tue, 12/09/2014 - 03:55

Using your approach:

its an FF relation with +3 lag. implies that activity b should finish 3 days after activity A finishes

 

L1, L2, L3 represent 3 day lag

A 1 2 3 4 5 6 7 8 9 10 L1 L2 L3
B         1 2 3 4 5 6 7 8 9
                           
Total days a+b 1 2 3 4 5 6 7 8 9 10 11 12 13

Hence total comes to 13 days.  Help me if this not correct

 

Gopi Krishna