Please help me with the below question.

Activity A has a pessimistic (P) estimate of 36 days, a most like (ML) estimate of 21 days, and an optimistic (O) estimate of 6 days. What is the probability that activity A will be completed in 16 to 26 days

A. 55.70

B.68.26

C.95.46

D. 99.73

Ans : B. I did calcuate Project variance but did not get a way to calculate probability of completed within variance.

## Time Management - Question

### Re: Time Management - Question

i think its d.

if u use P+M+O/3=21

or u use

P+4m+o/6=21

by both way its 21.

EAD is 21.

now deviation p-o/6=5

EAD-AD to EAD+AD

16 to 26 so its almost 100% (99.73%)

if u use P+M+O/3=21

or u use

P+4m+o/6=21

by both way its 21.

EAD is 21.

now deviation p-o/6=5

EAD-AD to EAD+AD

16 to 26 so its almost 100% (99.73%)

### Re: Time Management - Question

Answer B is correct ?

### Re: Time Management - Question

I believe Yes It is B from the explanation given. Below is the explanation

First, compute the standard deviation :σ =P-O/6 or 36-6/6=5 days Next, compute PERT expected time P+(ML)+O/6 or 36+4(21)+6/6=21 days Finally, determine range of outcomes using 1σ:21-5 = 16 days and 21+5 = 26 daysSimply defined, 1σ is the amount on either side of the mean of a normal distribution that will contain approximately 68.26% of the population.

Not sure of the source of this question though, from one of forwarded sheet.

First, compute the standard deviation :σ =P-O/6 or 36-6/6=5 days Next, compute PERT expected time P+(ML)+O/6 or 36+4(21)+6/6=21 days Finally, determine range of outcomes using 1σ:21-5 = 16 days and 21+5 = 26 daysSimply defined, 1σ is the amount on either side of the mean of a normal distribution that will contain approximately 68.26% of the population.

Not sure of the source of this question though, from one of forwarded sheet.

### Re: Time Management - Question

Duration=(6+21*4+36)/6 = 21

SD= (36-6)/6=5

Here we need to remember that the SD=1 Sigma.

68.26% of Confidence =1 Sigma = 1 SD = 1*5= 5 days; Range = 21 +/-5 = 16 to 26 Days

95.46% of Confidence = 2 Sigma =2 SD = 2*5= 10 days; Range = 21+/- 10= 11 to 31 days

99.73% of Confidence = 3 Sigma =3 SD = 3*5= 15 days; Range = 21+/- 15= 6 to 36 days

99.99985% 0f Confidence = 6 Sigma = 6 SD = 6 *5 =30 days = Not applicable.

Now the answer is B.

SD= (36-6)/6=5

Here we need to remember that the SD=1 Sigma.

68.26% of Confidence =1 Sigma = 1 SD = 1*5= 5 days; Range = 21 +/-5 = 16 to 26 Days

95.46% of Confidence = 2 Sigma =2 SD = 2*5= 10 days; Range = 21+/- 10= 11 to 31 days

99.73% of Confidence = 3 Sigma =3 SD = 3*5= 15 days; Range = 21+/- 15= 6 to 36 days

99.99985% 0f Confidence = 6 Sigma = 6 SD = 6 *5 =30 days = Not applicable.

Now the answer is B.

- AchalGupta
**Posts:**9**Joined:**Thu Mar 27, 2014 8:49 am

### Re: Time Management - Question

Ans- B

I also agreed with sunku calculation.

I also agreed with sunku calculation.

### Re: Time Management - Question

Thanks Sunku, this explains. So this is not really calculation should go by the definitions.

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