we have a 1/4 chance of each number for x and y, so there is a 1/16 chance for any given pair of numbers.
a list of all possible pairs:
0,0
0,1
0,2
0,3
1,0
1,1
1,2
1,3
2,0
2,1
2,2
2,3
3,0
3,1
3,2
3,3
since 0 is an invalid number for a triangle, there is a 7/16 chance for an invalid triangle already. we continue to cross out invalids. also, if the sum of any two side lengths of a triangle is not greater than the length of the third side, it is an invalid triangle. 1,2 and 2,1 is invalid, so we have 9/16 invalid. 2,3 and 3,2 are invalid, 1,3 and 3,1 are invalid, now we have 13/16 invalid. 3,3 and 2,2 are isosceles so they are valid, and we already said 1,1 was valid. there is a 3/16 chance you would get a real triangle with side lengths 1, x, and y. this is an example with fair four sided dice. if it is done with unfair dice, the results could vary greatly.