how many two numbers can be added to make twenty? combinations

we have to make a board game for school for young children adding up to twenty.#

We have made the game idea but need to know how many combination of two numbers added together make total of 20.  can you help?
in Statistics Answers by Level 1 User (120 points)

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There are 9 pairs of different numbers: 1+19, 2+18, 3+17, 4+16, 5+15, 6+14, 7+13, 8+12, 9+11. Two 10s also make 20, so if these are allowed, there are 10 pairs altogether.

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