What is the probability of someone correctly guessing your social security number? (assume all digits 0-9 are available for use)a

1 / 999,999,999

Explanation:

You can do it in two different ways.

1) First approach

probability = number of positive events / number of possible events

i) number of positive events = 1 (your number is just one number)

ii) number of possible events = number of valid numbers

Assuming the smallest valid number is 1, and the greatest one is 999,999,999, that leads to 999,999,999 different numbers

iii) probability = 1 / 999,999,999

2) Second approach

i) there are 9 digits.

ii) the guesser must guess all the digits in the correct order

iii) since there are 10 digits, from 0 to 9, there are 10 × 10 × 10 × 10 × 10 × 10 × 10 × 10 × 10 = 1,000,000,000 different combinations

But that includes the number 000,000,000 which is not valid, so you have to subtract 1: 1,000,000,000 - 1 = 999,999,999

Which leads to the same result of the first approach.

step-by-step explanation:

his chances of getting a coin of higher value is 4/19

step-by-step explanation: