Effective entry of fractions divided to multiple elements

Question

There are several resources divided into groups with different count (from 1 to 10). User has to enter an approximate usage of every resource in group, so average group cost can be calculated. This requires percentage utilization of resources inside the group, which is unknown, but user has to enter some assumption as ratio between them. In the following example average cost for Group A is 17.75, and Group B is 20.

                 Cost         Expected utilization
Group A
  Resource 1      10                   0%
  Resource 2      15                  80%
  Resource 3      25                   5%
  Resource 4      30                  15%
  Resource 5      40                   0%
Group B
  Resource 1      20                 100%
Group C
  Resource 1      20                 100%
  Resource 2      40                   0%

Note that cost of the resources gradually rises, but in different steps.

Sum for every group is considered 100% and user has to find the ratio, how to divide 100% to every resource.

Number of resources in group:
1   Nothing to divide
2   Simple slider 0-100%
3   ????

I want to avoid this kind of dialog:

^{download bmml source – Wireframes created with Balsamiq Mockups}

The question is, what UI design allows to enter those ratios with minimum effort?

I thought about some "one click & drag" interface like this:

^{download bmml source}

This doesn't work for following reasons:

• not working for 4+ resources (problem to set more than one resource to zero)
• it requires a lot of space
• when one resource outweighs the others, it is problematic to divide the smaller ones

Answer 1

As myself and others have mentioned recently, a good way to intuitively represent and modify percentages is a vertical bar chart with sliders/handles:

With (editable) numbers for each part. By default I'd set them to have equally large portions, so for group A, 20%, group B is a full 100% for one resource, and C is 50/50.

Answer 2

My summary what was implemented (client's decision):

All resources inside every group have some expected utilization. User has to divide that number among the resources in this dialog:

^{download bmml source – Wireframes created with Balsamiq Mockups}

"Remains" is the amount of required work decreased by already divided amount in resource fields. So user has to get to "Remains=0" state, when Average price is calculated and OK button is enabled. Dialog is used for groups with 2+ resources only.

Reasoning behind this decision:

User knows the exact absolute value he has to divide. So instead of rough percentage, he has to divide that absolute value down to zero. Then the weighted average can be evaluated and confirmed by dialog.

I am accepting PicelSnader's answer, thanx for help.