Answer: 1/(3,521,614,606,208)
Step-by-step explanation:
There are 26 letters in the English alphabet. This doubles to 52 when considering upper and lowercase letters. Then add on 10 more because of the digits 0 through 9.
In total, there are 2*26+10 = 52+10 = 62 different characters to pick from for any given slot of the 7-character password.
Assuming repeated characters are allowed, this then gives us
62^7 = 3,521,614,606,208
different passwords possible. This massive number is a little over 3.5 trillion. In scientific notation, it is approximately equal to 3.522 * 10^12
The probability of randomly guessing the correct password is 1 over that massive number, since there's only one way to get the correct password. We get the fraction 1/(3,521,614,606,208)
We can say the odds of guessing the correct password are roughly 1 in 3.5 trillion.