My math skills have declined rather rapidly. My question should be fairly simple. How do I calculate the chance of an occurance within probabilty. That probably didn't make any sense.

Let's say I create a random number between one and four and make a guess and count how many times I guess correctly. Probability is I guess correct 25% of the time. Let's say I guess ten million times. If my result is that I guessed right 30% of the time, how do I calculate the chance that that could occur? How do I calculate the standard deviation for such a case and how many deviations my result was?

Formulas would be great. Websites explaining this basic stuff would be great too (maybe help nudge my noggin back in place). Thanks.