Let's assume that he needs exactly 5 to reach home base. Anything bigger would be an overshot, anything smaller would be insufficient. So how many possible throws of two dice are there? There are 36, so this is all the possible outcomes, including permutations (the order of the dice).
How many ways can we get 5 with two dice? We can have 1-4, 2-3, 3-2, 4-1. That's 4 possibilities, so 4/36=1/9 are the odds of success and 8/9 are the odds of failure.
He should be nervous!