How to calculate expected duration, variance, and standard deviation of an activity

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Project Management Tutorial: How to calculate expected duration, variance, and standard deviation of an activity.
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[@kleopaskleopas3978]

It's people like you make me pay for my WiFi. Your unselfish contribution is highly appreciated. Thank you thank you soo much.

[@Engineer4Free]

Thanks Kleopas!!!! I appreciate your comment 😊

[@NeilTheBoss12]

You didn't waste any time and explained the concept clearly! I really appreciate it!

[@Engineer4Free]

Thanks Neil!! 🙌

[@killerhunt0]

So simple, but such a hard formula to find. My teacher made it sound way more complex than it actually is...Thank you!

[@Engineer4Free]

Yeah... just a weighted average of some predetermined industry values. Good luck!!!

[@learner7600]

Thank You So Much. Lots of Love from Pakistan. Tomorrow morning i have a exam of Project Mgt. (MBA). I was stressed but after watching your lectures. I am feeling confident. I am still looking for how to calculate Standard Deviation after critical path.

[@brainhub-xplorer8774]

thank you sir, you did a great job, this is exactly what 'am was looking for

[@MattLydon2010]

Again, Thank you for the clear explanation!

[@Engineer4Free]

Of course, you're welcome!!

[@salbil5511]

Your videos are a lifesaver Mr Engineer ,thank you soooooooooooooooooooooooooooooooo much, stay blessed!!!!!

[@Engineer4Free]

Thanks!! Plz share with some friends 😊

[@zabihullahsarwari1414]

Thank you for your nice video, i tried so much to find that, finally i found in your video, that was so much useful for me

[@Engineer4Free]

Zabihullah Sarwari Glad to hear that you found it helpful! I have many other free project management tutorials, you can check them out here: www.engineer4free.com/project-management good luck!

[@scorpioinny24]

Thank you, your videos have been very helpful.

[@Engineer4Free]

Thanks Josh, glad I can help you out 🙂🙂

[@makandesteventutorials]

Thank you so much. We treasure you as Ugandans

[@Engineer4Free]

Thanks for watching!! Fun and little known fact: I was in Uganda at the beginning of covid and ended up staying for 4 months in Kampala when the borders shut! Some of my Dynamics videos were made there

[@junemaxmusic]

Do you have a video on how to compute a, b and m?

[@sweetvibes4578]

Wow the best explanation so far! TY

[@Engineer4Free]

You're welcome!!! Thanks for watching, got some more PERT videos here: engineer4free.com/project-management =)

[@logicalkishore5624]

It's very smart explanation thanks a lot

[@Engineer4Free]

Thanks friend, glad you liked it ☺️

[@moussayoussef236]

thanks, very nice explanation.....

[@abdelrahmanmohammed3561]

You are a great man , Thank you.

[@Engineer4Free]

Thanks Abdel

[@therugbaddie5587]

You are the reason I passed my PM class. *italian forehead kiss* graciassss kind sir 😂

[@Engineer4Free]

hahaha thanks! Happy to help =)

[@aafigueiredo]

Could you please explain me this formula of Variance? Normally it is different. I cant find this one. Is it specific for PERT?

[@swisdom9117]

Omg THANK YOU!!

[@kingzai1314]

thank you sir.

[@artwithapramit8742]

For variance u can just do (tb-ta)/6

[@zergitaye9548]

It is really very good and helpful.....

[@Engineer4Free]

Thanks for letting me know!

[@muralisubramanian765]

The standard formula for calculating variance is the sum of the squared differences between each point and the mean divided by the number of points. The formula that you have used is different. Can you please clarify this? Thank you

[@cereal1862]

How do you calculate the variance when the optimistic and pessimistic durations are 95% estimates? This was my exam question.

[@sameerakhanzafarullah4668]

Thanks very much..!! Uh explained it clearly..!! D way uh explained it was fab..!! But I gotta doubt.. Did uh punch in d answers roughly..??!! Cuz I calculated & thr was a difference btwn ur answers & d answers tht calculator showed..!! Plz reply 2 ths..!!

[@alithegreatesta7085]

Thank you so muchhhhh!!!!!

[@Engineer4Free]

You're welcome, thanks for watching! :)

[@luciabrown4552]

How do you know what times are on the critical path?

[@racehorse87]

Can you calculate the SD of the whole path from A to G?

[@AmeerHamza-cy6km]

What is logic behind division by 6? Does it depend on number of activities?

[@mikemcmanus1574]

very helpful. doing a problem exactly like this. thanks

[@Engineer4Free]

Awesome, glad to hear it! Do check out engineer4free.com/project-management for the rest of the vids if you haven't already. Cheers!

[@mikemcmanus1574]

will do. are all the videos you have on youtube all of the videos you have on your site? or are there more on the site?

[@Engineer4Free]

All the same videos for project management are on youtube and website. If your looking at my other courses, sometimes you'll find stuff on youtube that isn't on the website yet, because I haven't made enough videos to warrant dedicating a whole page to it yet, but usually once I get at least 20 or so videos on a topic then I'll make a page for it on the website.

[@IndianRootsAmericanWings8132]

What if there are lags? What would be the maximum possible duration and how lags can effect the maximum possible duration?

[@Theresistance64]

You just saved my kiester with this explanation. My professor gave me 16 pages of calculations and somehow I was supposed to figure out which one of those was the calculation for the duration. Math is NOT my strongest subject.

[@Engineer4Free]

Haha glad I was able to help save your kiester =p

[@xav457]

Thanks

[@philippinebestmassage2024]

What is mean,variance and standard variation?

[@AshishThakur-qd7yj]

Please reply to my question. Why we calculate variance first and then standard deviation??

[@alvinramdin8900]

Forward Pass Method E1=0 E2=E1+t1,2 [t1,2=A=4.5]=0+4.5=4.5 E3=E2+t2,3 [t2,3=B=8.5]=4.5+8.5=13 E4=E3+t3,4 [t3,4=C=9.5]=13+9.5=22.5 E5=E3+t3,5 [t3,5=D=7]=13+7=20 E6=Max{Ei+ti,6}[i=45,] =Max{E4+t4,6;E5+t5,6} =Max{22.5+14.5;20+12.83} =Max{37;32.83} =37 E7=E6+t6,7 [t6,7=G=4]=37+4=41 Backward Pass Method L7=E7=41 L6=L7-t6,7 [t6,7=G=4]=41-4=37 L5=L6-t5,6 [t5,6=F=12.83]=37-12.83=24.17 L4=L6-t4,6 [t4,6=E=14.5]=37-14.5=22.5 L3=Min{Lj-t3,j}[j=54,] =Min{L5-t3,5;L4-t3,4} =Min{24.17-7;22.5-9.5} =Min{17.17;13} =13 L2=L3-t2,3 [t2,3=B=8.5]=13-8.5=4.5 L1=L2-t1,2 [t1,2=A=4.5]=4.5-4.5=0 The critical path of the project is : 1-2-3-4-6-7 and critical activities are A,B,C,E,G The total project time is 41

[@lanandmiraperryandgiles342]

How do you do that off a computer

[@youeclipseall]

If it just given one duration time (no ta, tm, tb), how do I calculate SD?

[@Engineer4Free]

Hmmm sounds fishy. If your dealing with SD in scheduling problems, then you are dealing with PERT problems and should be given ta, tm, tp. Or at least variance, which you could just take the square root of. Have you seen all my PERt videos? They are videos 39 - 46 here: engineer4free.com/project-management

[@user-kz7ds7hb9j]

Thank you sir

[@Engineer4Free]

You're welcome friend!

[@zccheah8267]

Just checking my understanding, the formula of "mean" is not a fixed at "divided by 6" I supposed? in this case you are choosing 6, as it it means our sample between ta, tm, tp distributed as below: ta, tm, tm, tm, tm, tp We could have different distribution pattern such as, ta, tm, tm, tm, tm, tm, tm, tp that makes us ta + 6tm + tp divided by 8?

[@Engineer4Free]

I suppose you could have a different distribution pattern for some reason, but with PERT problems like this unless otherwise mentioned, I would assume the weighted average assigns 4 to tm and 1 to the others

[@captainianmich1814]

Thanks.Though mean for b is 9.84

[@waynesaviour]

dude i love you. but whats the use of predecessor ?

[@mohamedelsheikh7900]

very helpful videos, thank you very much sir, i really need to know your name if it suits you of course, thanks again keep up the good work.

[@Engineer4Free]

Thanks for the comment! My name is Braden, you can learn a little bit about me here engineer4free.com/about

[@mohamedelsheikh7900]

not at all, you deserve it for sure

[@HarshVardhanM]

expected duration for the project will be the summation of mean for all the activities?

[@Engineer4Free]

For all activities along the critical path. Not all activities in the project.

[@peppeblus5189]

Hey! usually i have been given all 3 of the times however this time i have only been given the average duration as well as the SD for each activity. I am lost on how to solve the expected value of a project with the optimistic and pessimistic times? help would be much appreciated :)

[@joshemman]

The average duration will be the activity time (already calculated for you). To obtain the project variance, you square the individual standard deviations and add them together. You then take the square root of the project variance to obtain the project's standard deviation.

[@TomPatterson-xt3xn]

how do i even type 2 on the calculator cant even get the correct answer to follow along

[@larisawahlang6685]

How do you find the optimistic,most likely and pessimistic duration?

[@Engineer4Free]

I don't have any videos on coming up with those numbers, typically in PERT problems you will always be provided with those numbers and the focus of the question is to use them to find expected durations etc.

[@larisawahlang6685]

Engineer4Free Oh ok thank you

[@user-fp9ck5zs4i]

감사합니다.

[@Engineer4Free]

천만에요

[@PleAseStaANdBy]

What do I do if I don't have the pessimistic or optimistic durations?

[@Engineer4Free]

Then you are probably just looking at a more basic problem. See videos #4-9 here: engineer4free.com/project-management

[@strongyin5574]

great.

[@Engineer4Free]

Thanks ☺️

[@xodeproductio8339]

what happen when the estimated time is in decimals? My lecturer told me to round them up... so how to round ? if it 4.5 i take 4 or if it is 4.8 i take 5 ?I'm a little confused could you help me ? how does this works?

[@nefferbarragan7605]

What did yo do??

[@xodeproductio8339]

@@nefferbarragan7605 well, I didn't get an answer. So I skipped this question in exams 😅 sorry bro

[@elizabethfransamutenya477]

but why divide b six where is the 6 coming from. in calculating the Mean

[@Engineer4Free]

It's basically a weighted average. If you count up the t's in the expression you'll see that there are 6 (one ta, four tm, one tb). Taking the average of a set of numbers you add them up and divide by how many there are. This set of numbers artificially weighs tm 4 times more than each ta or tb. This 3-point time analysis is fundamental to PERT analysis. You can find all my PERT videos in the last section of the course at engineer4free.com/project-management or if you'd like to know more about the origins of the 3-point time analaysis, I'd just recommend googling for keywords like PERT, PERT 3 point time analysis, Project Management Mean Time, etc... Hope that helps, cheers.

[@andrunieharris1827]

So standard deviation is almost the same formula as variance; in that you don't "square" the result from the bracket.....standard deviation = [(tb - ta)/6]......?

[@Engineer4Free]

Yeah basically

[@mirimtiazadnan9310]

Andrunie Harris Thanks man... :)

[@SepSol75]

do you have any videos on GERT and PN ?

[@Engineer4Free]

You can find all of the PM videos that I made at engineer4free.com/project-management

[@azizdafaputra3163]

sir, what if there is no tm. Just ta and tb?

[@Engineer4Free]

Hmmm strange, you should probably be given them all. Is it disguised somewhere else in the question?

[@pseegamer3481]

Tankyou

[@Engineer4Free]

wlcome

[@nicolegarcia4901]

how do you write this in excel spread sheet? I keep getting a different answer

[@Engineer4Free]

You'll just need to take care with all the brackets and functions that you use.

[@moussayoussef236]

@@Engineer4Free you should find the same number, you need to try it....

[@ammarelmazi8370]

Why is it always dividing by 6 ? Can someone explain ?

[@Engineer4Free]

Expected duration is a weighted average of ta, tm, tb, not just a pure average. To find average of some values, we add them up and divide by the number of values. A pure average of them would be (ta + tm + tb)/3 but instead we do (ta + 4*tm + tb)/6. We sum 6 values (1+4+1=6) and divide by 6. This gives a tm a stronger influence in the average, or otherwise makes it a weighted average.

[@ammarelmazi8370]

Thank you!

[@anilkumarsaini4148]

Show the question and how you get to, tm , to

[@Engineer4Free]

ta, tm, and the are typically industry determined values that will be provided to you. No need to calculate. They would be determined by research and observation form past works IRL.

[@yolandantshakala9545]

How do you calculate the optimistic most likely and pessimistic..or you just estimate using the duration on the gantt chart as your optimistic.

[@pearlgemegah2380]

why is the SD divided by 6?

[@Engineer4Free]

The SD isn't divided by 6, do you mean μ? It is just a weighted average that gives 4x more emphasis on the most probable time than the other two.

[@yuzarsifsalim7896]

@@Engineer4Free why did you divide by 6 in finding mean

[@Engineer4Free]

mean is another word for average. When you take average of some numbers, you add up the numbers and divide by how many there are. This is a weighted average consisting of 6 numbers. (one ta, four tm's, and one tb). The mean (or average) is the sum divided by six. Make sense? It's weighted because by multiplying tm by 4 we are artificially giving it more emphasis.

[@ManningOWNsTeboww]

@@Engineer4Free So it's always going to be 6?

[@Engineer4Free]

@@ManningOWNsTeboww yeah

[@finalboss8624]

values of all ur variances and standard deviations are wrong 9-2 is 7 and 7/6 is 1.16 which is standard deviation and 1.16 x 1.16 is 1.3456 which is variance

[@finalboss8624]

If I'm Wrong pls correct me