Question

If you roll a number cube twice, how many unique combinations are there?

Answer 1

That depends on the numbers on the cube.

If you mean "roll a fair 6-sided die" twice then:

All 36 combinations:

(1,1), (2,1), (3,1), (4,1), (5,1), (6,1)
(1,2), (2,2), (3,2), (4,2), (5,2), (6,2)
(1,3), (2,3), (3,3), (4,3), (5,3), (6,3)
​(1,4), (2,4), (3,4), (4,4), (5,4), (6,4)
(1,5), (2,5), (3,5), (4,5), (5,5), (6,5)
​(1,6), (2,6), (3,6), (4,6), (5,6), (6,6)

Unique combinations:

(1,1), (2,1), (3,1), (4,1), (5,1), (6,1)
(1,2), (2,2), (3,2), (4,2), (5,2), (6,2)
(1,3), (2,3), (3,3), (4,3), (5,3), (6,3)
​(1,4), (2,4), (3,4), (4,4), (5,4), (6,4)
(1,5), (2,5), (3,5), (4,5), (5,5), (6,5)
​(1,6), (2,6), (3,6), (4,6), (5,6), (6,6)

36 - (5 + 4 + 3 + 2 + 1)

36 - 15

21 unique combinations

Answer 2

6^2=36 combinations are there

Pre Algebra - http://www.mathcaptain.com/algebra/pre-algebra.html