Using extracredits the calculation creates unexpected results.
Based on some discussions in the German translation group we found there should be two different types of calculations with extra credits we can edit.
1) extra credit points are added for an Item to the median of the standard tasks (items) = (Item1x2)+(((Item2+Item3)/2). These are additional points for the students because he solved an additional task.
2) The weighting of one item should be higher than the other and it creates credit points in this way. (Item1x2)+((Item2+Item3)/3).
The calculation described in the help file gives Item 1 a very height weighting.
Here is the example from the help file:
<li>Item 1 is graded 0-100 and its "Extra credit" value is set to 2</li>
<li>Item 2 is graded 0-100 and its "Extra credit" value is left at 0.0000</li>
<li>Item 3 is graded 0-100 and its "Extra credit" value is left at 0.0000</li>
<li>All 3 items belong to Category 1, which has "Mean of grades (with extra credits)" as its aggregation strategy</li>
<li>A student gets graded 20 on Item 1, 40 on Item 2 and 70 on Item 3</li>
<li>The student's total for Category 1 will be 75/100 (20*2 + 40 + 70) / 2</li>