As an administrator, go to the "Home > System Settings" page. Click on the "Defaults" (1) tab and go to the "Question weight per difficulty" (2) section. 

Here, you can see four fields where you enter a question weight for each one of the four difficulty levels (Low, Medium, Hard, Very hard). Each value can be set from "1" to "9" and, when calculating the unit's final grade, it proportionally affects the weight of each answer (right or wrong) in relation to the others.

For example, if you enter the values 1,2,4, and 8, then the weight of "Medium" difficulty questions is 2, double the weight of "Low" difficulty questions which is 1. Likewise, the weight of "Very hard" questions is 8, double the weight of "Hard" questions, 4 times the weight of "Medium" difficulty questions and 8 times the weight of "Low" difficulty questions.

After setting your new weights, don't forget to enable the "Update current weights" option (3) to overwrite the previous ones. Finally, click on "Save" (4) to proceed.

In the following example, we have set our weights to 1 for "Low, 2 for "Medium" and "Hard", and 5 for "Very hard" (5).

Now, let's create a test with 1 question for each difficulty level. The "Low" difficulty question will have a weight of 10%, the "Medium" and "Hard" will have a weight of 20% each, and the "Very hard" question will determine the test's final score by 50%. Depending on the test's settings, the weight each question carries is shown to learners as a percentage while taking the test:

In the same way, the weight each question carries is also shown to learners after completing the test.

Note: You have now set a default weight for one or more difficulty levels so that you don't have to set it manually for each new question. However, if necessary, you can change it manually for any question you create or import (6).