How many single digit addition problems per minute should someone be able to do before doing multiple digits?

Question

Remember that the person I'm teaching Is quite sedated.

Answer 1

Well I have heard it is 3 seconds for each one, so for a minute it is  20

Answer 2

Doing math isn't  about speed.  Knowing basic math facts is a tool to make the computation  easier.  Using timed tests for math facts is a common way to have students become fluent with their facts.  

You mention that the person is sedated makes your question difficult.  I give 30 problems in 3 minutes in a  regular education 4th grade class.  I suggest you give tests of increasing difficulty and move students to the more difficult test as they master each test.