You forget the last two digits of your password for a website.

a. What is the probability that you randomly choose the correct digits?

$$
Question 2
Write the probability as a percent.
This is
%.
Question 3
b. Suppose you remember that both digits are even. How does this change the probability that your choices are correct?
Responses

It increases the probability that your choice is correct to

, or 4%, because each digit could be 0, 2, 4, 6, or 8.
It increases the probability that your choice is correct to 1 over 25, or 4%, because each digit could be 0, 2, 4, 6, or 8.

It increases the probability that your choice is correct to

, or 20%, because each digit could be 0, 2, 4, 6, or 8.
It increases the probability that your choice is correct to 1 fifth, or 20%, because each digit could be 0, 2, 4, 6, or 8.

It increases the probability that your choice is correct to

, or 50%, because even numbers make up half of the available numbers.
It increases the probability that your choice is correct to 1 half, or 50%, because even numbers make up half of the available numbers.

Knowing that both digits are even does not affect the probability that your choice is correct because the same number of choices exists.
Knowing that both digits are even does not affect the probability that your choice is correct because the same number of choices exists.

1 answer

To determine the probabilities for the two parts of your question, let's analyze them one at a time.

Question 1

a. Each digit in the password can be any number from 0 to 9, giving us a total of 10 possible choices for each digit. If you forgot the last two digits, the total number of combinations for the two digits is:

\[ 10 \times 10 = 100 \]

If you are randomly choosing two digits, only one of those combinations is correct. Therefore, the probability of randomly selecting the correct two digits is:

\[ \frac{1}{100} = 0.01 \]

To express this as a percent, we multiply by 100:

\[ 0.01 \times 100 = 1% \]

So, the probability that you randomly choose the correct digits is 1%.

Question 2

The probability as a percent is:

1%.

Question 3

b. If you remember that both digits are even, you are reducing your options. The even digits available are 0, 2, 4, 6, and 8, making a total of 5 possible choices for each digit. Thus, the total number of combinations for the two even digits is:

\[ 5 \times 5 = 25 \]

Since there is still only one correct combination, the new probability of randomly selecting the correct even digits is:

\[ \frac{1}{25} \]

To express this as a percent, we multiply by 100:

\[ \frac{1}{25} \times 100 = 4% \]

So, it increases the probability that your choice is correct to 1 over 25, or 4% because each digit could be 0, 2, 4, 6, or 8.

Thus, the correct response from the provided options is:

"It increases the probability that your choice is correct to 1 over 25, or 4%, because each digit could be 0, 2, 4, 6, or 8."