Assuming that the number cube has six sides, the answer would be 50%.
Explanation:
If you rolled a three on a six sided number cube once and were about to make another roll hoping for it to be an even number, you'd only get the chance of three considering there are three even and odd numbers on the cube. Knowing that the favorable outcomes are 3 and the normal outcomes are 6, you'de divide them and get 0.5. Then multiply by 100.