what are the numbers 1-20 in a base twelve number system?

Answer 1

First you need 12 symbols to represent the "digits" in the base 12 number system. These would be 0, 1, 2, 3, 4..., 8, 9, A, B.

So now you have the numbers up to 11. When you get to 12 you have to "carry" a 1.

12 = 10 (base 12)
13 = 11 (base 12)
14 = 12 (base 12)
15 = 13 (base 12)
16 = 14 (base 12)
17 = 15 (base 12)
18 = 16 (base 12)
19 = 17 (base 12)
20 = 18 (base 12)

I see you are posting numerous questions on bases, so I suggest you do a little more studying on the topic rather than just asking for the answers. Good luck on your future tests.