Scoring of multiple-selection/drag & drop questions etc

Where a question has multiple correct responses I want the test-taker to be scored for every correct response they make not just that they get all responses correct to get a score for the question. For example:

How many colours are in the Canadian flag:

- Red

- Blue

- White

- Black

- Green

Here the test-taker should get points for selecting red and white but they should also get points for not selecting green, black and blue. Furthermore, I am not sure what should happen if they select one of the incorrect responses or if they don't select one of the correct reponses.

Can you tell me how this is calculated? We have a vendor who can implement this but we just need to establish how it is done. 

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