Calculating The Critical Path

Video Activity

This lesson offers an example of calculating the critical path. For example, there are activities A,B and C; Activity C cannot happen until A and B are complete. In this lesson, the instructor uses the whiteboard to draw a diagram to demonstrate the process of calculating a critical path. In calculating a critical path; there are a few methods: For...

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Time
5 hours 14 minutes
Difficulty
Intermediate
CEU/CPE
10
Video Description

This lesson offers an example of calculating the critical path. For example, there are activities A,B and C; Activity C cannot happen until A and B are complete. In this lesson, the instructor uses the whiteboard to draw a diagram to demonstrate the process of calculating a critical path. In calculating a critical path; there are a few methods:

  • Forward pass
  • Backward pass
  • Calculating stock
  • Critical Path

[toggle_content title="Transcript"] An example of calculating the critical path, as you know each one of these activities. You are going to say activity A, B, C, D, and E. Then, I will give duration to each one of these. Activity A could make up a number four, three, seven, two four. Then I will give an example of C requires B and A to be finished. Then I am going to say D requires A to be finished. E we say...E requires D and C to be finished. There are so many ways I can write this. All you are going to do is you are going to take this data and you are going to create a block diagram for this. What I will like to do is first knowing A is four days and then B can also be at the same level. B is three days. Next am looking at C. C requires A and B to be finished. I know to draw that like this. The duration for C is seven. D requires A to be finished...has nothing to do with B or C just A then it takes two days. E requires D and C to be finished so D and C are right here so and it requires to be finished. I am going to draw E right there and E takes four days. The first thing I want to do forgo how long this takes. I want to do a forward pass. I start of f in day one. A and b start off in day one. A is one plus four minus one. Remember, start off on a Monday so Monday Tuesday, Wednesday, Thursday. I am going to finish on a Thursday not on a Friday so you going to remember to subtract the one. B starts off in day one so Monday, Tuesday, and Wednesday. So it is one plus three minus one. In between tasks if it ends on the third day, I have to start on the fourth day. C requires both of these to be complete so I take the higher number. This is four plus one, which gives me five. D requires only A to be complete so four plus one is still five. D takes two days so five plus two minus one gives me six. C takes seven days five plus seven minus one. What would that be eleven? E requires both C and D to be complete in order to start so I have to go the higher number. It is going to start on the twelve day. Eleven plus one is twelve. E takes four days minus one so fifteen. That is the forward pass so to complete this project I know it is going to take fifteen days. Now I am going to give the backward pass. What the backward pass allows me to do is forgo slack. If it's on the critical path, we will have a little room in case anything goes wrong. I want to take this fifteen so doing the opposite. So it's fifteen minus four plus one. Good way to checking yourself is if you know you are on the critical path this numbers, fifteen minus fifteen is going to be zero. Twelve minus twelve is going to be zero. This twelve, I am going to subtract one I come up with eleven. If you notice D, it is six here but am transferring this to eleven so D is not on the critical path which make sense if its only taking two days unless it is taking seven days. Eleven minus two plus one is ten, eleven minus seven plus one should be five. I am going to take the lowest number and subtract one so this will be four. Doing the same method four minus four plus one gives me one. Four minus three plus one gives me two. I can actually start B on the second day. I don't need to start on the first day. The way I found out that is I take...doesn't matter which one this minus this or this minus this. That gives me one day of slack. This is on the critical path so there is zero slack. For this, one doesn't matter which sign I say ten minus five gives me five. So I have five days of slack there and this is on the critical path. Sometimes I ask you what critical path is, and you are looking for that zero slack, I would say A-C-E-ACE. That would pass me one of the multiple choice answers for this question or I might ask you would is the slack for D, or I might give where the problem is...what is the latest D can start on in order for the schedule. [/toggle_content]

Video Transcription
00:04
an example of calculating the critical path is you know, each one of these activities. So I'm going to say activity a
00:11
hey,
00:13
see
00:14
day
00:16
and e.
00:17
And then they're gonna give you durations for each one of these.
00:22
So activity A could be
00:24
make up a number for
00:27
37
00:29
two,
00:30
four
00:32
and then they're going to give you an example of
00:35
see requires be
00:39
and a
00:41
two
00:42
be
00:43
finished.
00:45
Then they're gonna say
00:49
D
00:51
requires
00:53
hey,
00:54
to be
00:56
finished,
00:58
I don't see e will say
01:00
e requires
01:06
day and see
01:08
to be
01:11
finished. There's many ways that can write this,
01:14
but
01:15
all you're gonna do is I'm gonna take this data
01:18
and you're going Thio,
01:21
uh,
01:22
create a block diagram for this.
01:25
So what I'd like to do is first knowing that
01:29
a is for
01:30
days and then
01:34
be
01:34
can also be at the same level.
01:37
Being is three days.
01:40
So next I'm looking at sea. So see requires A and B to be finished.
01:46
So I know
01:49
to draw that like this
01:49
and then duration for see this seven
01:56
de requires a to be finished.
01:57
That has nothing to do with beer. See, just a
02:01
then it takes two days
02:06
E requires a d and C to be finished. So
02:09
DNC air right here. And it requires
02:13
then to be finished
02:15
so that I know to draw e
02:20
right there.
02:21
And he takes four days.
02:23
So the first thing I'm gonna dio is figure out how long this takes. I'm gonna do a forward pass.
02:28
So I start off on day one.
02:30
So a and be able to start off on day one
02:32
A is one plus four minus one
02:37
member.
02:38
Start off on a Monday. So Monday, Tuesday, Wednesday, Thursday Someone have finished
02:45
on a Thursday,
02:46
not under Friday. So you gotta remember to subtract the one
02:50
be
02:52
starts often day once on Monday,
02:53
Tuesday, Wednesday.
02:55
So it's one plus three minus one
03:00
and then in between tasks,
03:02
if it ends on
03:05
the third day, I have to start on the fourth day.
03:07
But
03:08
see requires both of these to be complete,
03:12
So I take the higher number.
03:15
So this is four plus one, which gives me five.
03:20
De requires only a to be complete.
03:24
So four plus one is still five
03:29
d takes two days,
03:31
so
03:32
five plus two minus one gives me six
03:36
c takes seven days,
03:38
five plus seven minus one.
03:42
What would that be? 11.
03:46
And then e requires both c and D to be complete
03:52
in order to start.
03:53
So I have to go the higher number.
03:55
So this will start on the 12th day.
03:57
11 plus one is 12.
04:00
Then he takes
04:01
four days
04:03
minus one.
04:05
So 15
04:08
that's the forward pass.
04:10
So they complete
04:11
this project.
04:12
I know it's gonna take 15 days.
04:15
Now I'm going to do the backward pass on what the backward pass allows me to do is figure out slack.
04:21
So if it's on the critical path where I have a little bit of, ah,
04:26
wiggle room in case something goes wrong,
04:29
So I want to take this 15.
04:32
So it's doing the opposite. So it's 15 minutes four plus one.
04:39
Good way of checking yourself is if you know you're on the critical path.
04:42
These numbers 15 minus 15 is gonna be 0 12 on his 12 is gonna be zero.
04:47
Um, so this 12
04:49
I'm gonna subtract one. I come up with 11.
04:54
Well, if you notice d, it's six hair, but I'm transferring this 11
04:59
so d is not on the critical path. What's makes sense if it's only taking two days and this is taking seven days,
05:06
So 11 minus two plus one is 10
05:11
11 minus seven
05:13
plus one
05:15
should give me five
05:18
and then
05:20
I am gonna take the lowest number.
05:24
It's attract one.
05:25
So
05:28
this would be four.
05:30
This would be for
05:34
then doing the same method. So four minus four plus one because we won four minus three
05:42
plus one.
05:44
It is me too,
05:45
So I could actually start be on the second day. I don't need to start on the first day. The way find that out is,
05:53
um I take
05:54
it doesn't matter what's one
05:56
this
05:58
minus this
06:00
or
06:00
this Minus
06:02
this.
06:04
So that is being
06:05
one day of slack.
06:09
Um,
06:11
this is on the critical path, So there's zero slack
06:14
for this one.
06:15
It doesn't matter what side
06:16
I'll say
06:18
10 minus five. So 10
06:23
minus five is mi five.
06:26
So I have
06:27
five days of slack there,
06:30
and this is on the critical path.
06:32
So sometimes ask you
06:33
what is the critical path and you're looking for that zero slack. So I would say
06:40
a
06:41
see
06:43
Hey, ace.
06:44
So that would
06:46
has to be one of the multiple choice answer for for this question.
06:50
Or they might ask you what is the slack for D like? Give me a word. Problem is,
06:57
um,
06:58
what's the latest deacon start on and not affect the schedule?
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