How the hell did he crash this project?

Submitted by aliweb on Sun, 08/19/2012 - 02:29

The following question (see image below) is from Farndale's 262 free questions. I can't seem to understand how come the answer is C.

According to the explanation given he is crashing activity START and D thus saving $13000. But how the hell did he come up with that? He is asking "what is the least cost to crash the schedule to 10 days" and for that he is adding "Normal Duration" + "Crashed Duration" of both START and D activities to come up with 10 days!??

i.imgur.com/lyrJ7.jpg

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PMP / CAPM exam Question bank
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mvpmpwannabe

Sun, 08/19/2012 - 03:20

 I believe the answer is because you want to crash an activity (activities) on the critical path. The critical path is start, B, D, end and equals 12 days. To "crash" to 10 days, you need to look at one or more of these three activities. The least expensive, and gets you to 10 days, is crashing Start (saves 1 day/cost$8000) and D (saves 1 day/cost$$5000) for a total savings of 2 days at a cost of $13000. I believe Rita says to crash the activity closest to the end to help ensure meeting your completion date. I'm still studying tho so hopefully someone can confirm my thoughts or correct me. Good luck on your studies!

sspawar

Sun, 08/19/2012 - 05:46

  Crashed Durations = means new/revised durations (after subtraction)    
                   
  Answer is true            
      ACTIVITIES ORIGINAL
DURATION		 MINIMUM
POSSIBLE
DURATION
AFTER
CRASHING		 RELATIVE
COST OF CRASHING DAYS		 MAXIMUM
POSSIBLE CRASHING
DAYS		 FOR 10
DAYS @ MINI COST		  
      START            
    ACTIVITIES S  2 1 8000 1 1  
    A 5 4 10000 1 5  
    B 6 4 12000 2 6  
    C 4 3 12000 1 4  
    D 4 3 5000 1 3  
    E 3 2 5000 1 3  
      FINISH            
      PRO DU 12DAYS 8DAYS     10DAYS  
                   
                   
        5   4      
      A   C      
START   S            
    2, 1@8000 B   D     FINISH
        6    4 ,3@5000      
                   
ALL THREES PATHS ARE HERE @ CRITICAL PATH  E      
  1 ST,S,A,C,FI 10DAYS     3      
  2 ST,S,B,D,FI 10DAYS            
  3 ST,S,B,E,FI 10DAYS            

aliweb

Sun, 08/19/2012 - 09:14

But the question says "crash the schedule to 10 days" and task START and D will only save 2 days. I am not been able to understand this part.

Total normal duration is 24 days while Total crash duration is 17 days which means even if we crash all activities we will only say 7 days!?

sspawar

Sun, 08/19/2012 - 10:29

prepare network diagram according to conditon given.

dont add simplya+b+c +------

see in detai again

      ORIGINAL CASE        
        5   4      
      A   C      
START   S            
    2   B   D     FINISH
        6   4      
                   
ALL THREES PATHS ARE HERE    E      
  1 ST,S,A,C,FI 11DAYS   3      
  2 ST,S,B,D,FI 12DAYS @ CRITICAL PATH       
  3 ST,S,B,E,FI 11DAYS Here project duration is =2+6+4 =12days
                   
      MAXIMUM POSSIBLE GIVEN with crashing  
        4   3      
        A   C      
START   S            
    1   B   D     FINISH
        4   3      
                   
ALL THREES PATHS ARE HERE    E      
1 ST,S,A,C,FI 8DAYS @ CRITICAL PATH  2      
2 ST,S,B,D,FI 8DAYS @ CRITICAL PATH         
3 ST,S,B,E,FI 7DAYS   Here project duration  =1+4+3=8 days
                   
                   
      To finish project in 10days  =     
        5   4      
      A   C      
START   S            
    2, 1@8000 B   D     FINISH
        6   4, 3@5000      
                   
ALL THREES PATHS ARE HERE @ CRITICAL PATH  E      
  1 ST,S,A,C,FI 10DAYS   3      
  2 ST,S,B,D,FI 10DAYS          
  3 ST,S,B,E,FI 10DAYS          

 

aliweb

Sun, 08/19/2012 - 11:28

Oh yes now I got it!

I didn't realize about network diagram and was just looking at the table to crash activities. Thanks for the explanation.

chullan88

Tue, 07/01/2014 - 06:43

Why can't activity B be crashed?

It has the least cost..

Any explanations...

cssk

Tue, 07/01/2014 - 19:35

Activity B costs 12k$ and gives you two days...I would say B is the correct answer!

chullan88

Thu, 07/03/2014 - 10:39

Hi cssk,
I understood the question later.
The point to be remembered is that after crashing,there shouldn't be any path with duration greater than 10.

That's why B cannot be the answer.