5253/5255
Since there are 2 defective bolts out of every 5255 bolts, that means that there's 5255-2 = 5253 good bolts out of every 5255 bolts.
So the probability of a good bolt is 5253/5255.
Now you need to reduce the fraction to it's simplest form.
The factors of 5255 = 5 * 1051
The factors of 5253 = 3 * 17 * 103
Since they don't have any factors in common, the fraction 5253/5255 is already reduced. So the answer is 5253/5255
