# Task duration with several resources

• ### Question

• Hi all. I created a task with a duration of 10days with 3 resources 100%. This duration corresponds in reality to 80H of effective work. When reducing the availability of 1 of the 3 resources down to 10%, MS project changed the duration to 100 days instead of 14.3 days. I tried all combinaisons of type, none of them is giving me the expected result. Did I miss something here? an option or configuration? .thx

Saturday, March 3, 2018 9:57 AM

### All replies

• Yes, you missed something.

Assuming standard calendar with working hours 08:00 - 12:00 and 13:00 - 17:00, 3 resources at 100% in 10 x 8 hour days should be 240 hours of work. You want it to be 80 hours of work. Assuming that you want each resource to have the same work, you need to change each of their assignments to 33.3%.

Use assign resources button on the resource tab ribbon.

The task has two settings which determine the outcome when you do this. They are the task type and effort driven. You can see these in the advanced tab of task information. I think you need them to be fixed duration, effort driven off. There are only 5 possible combinations which are fixed units, fixed duration or fixed work and effort driven is either on or off, except that it is always on for fixed work, so only 5, not 6.

Alternatively, instead of changing the assignment in the resource dialog, use the task usage view to input the work for each person.

How, exactly, did you reduce the availability down to 10%? Why 10%?

Where does 14.3 hours come from?

I have no idea what you mean by "in reality". Or "effective work". There is just work. It comes in three flavours, baseline, actual, remaining.

Any help so far?

Saturday, March 3, 2018 2:40 PM
• OK, my mistake. The total number of hours is 240H. But is here not the problem.

I have not initially asked a lesson for the beginners, I asked for a problem solving.

I start again my explaination:

I create a task of 240H with 3 resources 100% that I enter in the "resources" field.   The duration is 10 days.

I learn that one of my resources will only be 10% available. The 2 others still remain 100%.

I modify the concerned person by changing 100% down to 10% in the "resources" field.

Then the 240H of work should be executed in 14.3 days (exactely 14.2857)  instead of 10d (calculation).

What I don't understand is why MS Project is changing the duration from 10d to 100d (that would correspond to all 3 resources at 10% instead of 1 of them) instead of 14.3 days.

Sunday, March 4, 2018 10:29 AM
• thvernet38,

The problem is your expectation that Project is smart enough to re-allocate work between resources when you make one of them less available.  i.e.

1. Resources r1, r2, r3 all initially assigned at 80 hours each for 10 days.

2. Resource r3 "availability" reduced to 10%.  Resources r1 and r2 pick up the slack and end up working 114+ hours each, compared to Resource r3's 11.4 hours.  The task will be finished in 14.3 workdays.

Project's interpretation:

1. Resources r1, r2, and r3 each have individual skills that cannot be replaced by either of the other two.  The task requires 80 hours of the specialized work of each of the three resources.

2. Resource r3 may now only work 48 minutes per day to accomplish his 80 hours of work.  That will take him 100 days.

3. A look at the Task Usage view will reveal that the r1 and r2 finish their 80 hours of work each in 10 days.  The task is stretched out solely as a result of r3's distraction.

Conclusion: there is no combination of task type and effort driven that will give you the behavior you expect.  Project will never shift work from one assignment to another - that is the PM's job.

If the three resources truly are interchangeable, then you might consider making a single resource with availability of 300%, subsequently reduced to 210%.  That would give you the behavior you expect.  Trevor can supply some arguments against this approach based on his own experience.

Good luck, tom

Sunday, March 4, 2018 3:01 PM
• OK, good question. I use MSP2010.

I recreated what you say you did. Also tried all task type and effort driven combinations, except fixed duration because that is definitely not what you are after. Resources are A, B and C. The default task type is fixed units and effort driven is off. This is the MSP2010 default. MSP holds the work at 240 hours, holds A's work at 80 hours, assigns A at 0.8 hours (1/10 of 8) for each day, adjusts duration to 100 days to soak up A's 80 hours.

This calculation is correct, sort of, even if it is not what is expected.

I don't see how MSP can do anything else without more information.It definitely is not cutting B's and C's assignment to 10%. I get why you say it should be 14.3 days.

14.3 x 8 = 114.4
2 x 144.4 = 288.8 for B and C
10% of 114.4 = 11.44 for A
288.8 + 11.44 = 240.24

https://social.technet.microsoft.com/Forums/ie/en-US/cfc32c37-a159-4ccc-b49b-bb2cd910e3c8/how-to-get-ms-project-2010-to-auto-calculate-percentage-resource-allocation?forum=projectprofessional2010general

If you re-set the duration to 14.3 days, with task type = fixed work, A's work is 5.6 hours per day except for the last day which is 1.62 hours, but A's assignment units stay at or at least still displays 10%. It can't change resource assignment units. You are onto something and I don't much like it either.

I am tempted to fire up my other computer and try the same thing in MSP2003 and MSP2007. But it is late now, so I'll get back to you in the morning.

Sunday, March 4, 2018 3:24 PM
• Just to make things a bit more complicated, resource names field and the assign resources dialog both display A[10%] but peak units in the resource sheet displays 70%.
Sunday, March 4, 2018 3:29 PM
• Hi Trevor and Tom.

Many thx for your feed-backs and help. I woundered about the tool limitation and you confirmed it. I use MSP2013.

In reality in my "expedition" project I have around 100 tasks like this one (shared between several people who are not 100% assigned (such as 20%/50%/30% or else). I have to play with the assignment of resources to the different tasks in order to find the correct  combinaison to optimize the schedule.

I had already used tasks with several resources with less than 100% availability in the past, but I think I had not to change the % in between and have not noticed this tool limitation.

I will have to find another methodoly to build my schedule.

Thanks  again. Thierry

Monday, March 5, 2018 7:56 AM