Question

You have a combination lock that has the numbers 1-40 on the dial. You

forgot the combination, but you remember that the combination is three
numbers, the last digit of all three numbers is 6, and none of the numbers
are between 1 and 10. You make a random guess with what you know.
What is the probability that you will get the combination?

Answer 1

1/870 ≈ 0.0011494 or about 0.115% (rounded to 6 decimal places)

Explanation:

The first digit can be any of the numbers between 10 and 40, except for those that end in 6 (since the last digit of all three numbers is 6). This leaves us with 30 numbers to choose from for the first digit. Similarly, the second digit can be any of the numbers between 10 and 40, except for those that end in 6 and the one chosen for the first digit. This leaves us with 29 numbers to choose from for the second digit.

For the third digit, we have only one option since we know it ends in 6.

So the total number of possible combinations is:

30 * 29 * 1 = 870

Out of these, only one combination is the correct one. Therefore, the probability of guessing the combination correctly on the first try is:

1/870 ≈ 0.0011494 or about 0.115% (rounded to 6 decimal places)