A combination lock requires a user to select three numbers to unlock it, where all three numbers are between 1 to 30, inclusive. What is the probability someone can guess the correct combination given 100 attempts?

you can repeat numbers

3 numbers between 1 to 30 including 1 and 30

that means (30-1) + 1=30 numbers

3 slots that can be repeated

so there are 30^3=27000 combinations

in 100 attempts, hmm

that is a 100/27000=1/270 chance or about 0.37% chance