Question

A quick quiz consists of a multiple-choice question with 5 possible answers followed by a multiple-choice question with 5 possible answers. If both questions are answered with random guesses, find the probability that both responses are correct. Report the answer as a percent rounded to two decimal place accuracy. You need not enter the "%" symbol. Probability = %

Answer 1

Probability = 4%

Explanation:

For each answer, there are only two possible outcomes. Either it is correct, or it is not. The probability of an answer being correct is independent of other answers. So we use the binomial probability distribution to solve this question.

Binomial probability distribution

The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

`P(X = x) = C_(n,x).p^(x).(1-p)^(n-x)`

In which
`C_(n,x)` is the number of different combinations of x objects from a set of n elements, given by the following formula.

`C_(n,x) = (n!)/(x!(n-x)!)`

And p is the probability of X happening.

Each question has 5 possible answer:

The person guesses, so
`p = (1)/(5) = 0.2`

2 questions:

This means that
`n = 2`

Find the probability that both responses are correct.

This is P(X = 2).

`P(X = x) = C_(n,x).p^(x).(1-p)^(n-x)`

`P(X = 2) = C_(2,2).(0.2)^(2).(0.8)^(0) = 0.04`

As a percent:

Probability = 4%