Remember, addition can be done in any order, so look for pairs that make 10 to make these easier. Printable answer page after 10 questions.
Add the nearest multiple of 10 and then adjusting is a good way to do these: eg add 49 by adding 50 and subtracting 1.
Sometimes adding can be done by multiplying and then adjusting. Try these.
Add the four numbers on the shirts as quickly as possible. Only 60 seconds to complete as many as possible. 20 would be a very good score.