You took a test with 40 multiple choice questions.

permaneceerc

permaneceerc

Answered question

2021-09-20

You took a test with 40 multiple choice questions. Each question had 5 choices. What is the probability that you get at least 28 questions correct if you guessed in all of them.

Answer & Explanation

Benedict

Benedict

Skilled2021-09-21Added 108 answers

Step 1
NOTE: We will use binomial probability to solve this question. I will round off the results to 4 decimal places.
We have, The formula for binomial probability is as follows:
P(X=x)=C{x}npx(1p)nx, where
n= total number of trials
x= number of success
p= probability of success
We are given,
n=40
x=28
As there are 5 choices for each question, hence probability of one success is 1/5, i.e, 0.2. Hence p=0.2
Step 2
In this cade, we need to find P(X28). The calculations for the required probability is as follows:
P(X28)=x=2840C40x(0.2)x(10.2)40x
=0.00000001
0
Hence, the probability that you get at least 28 questions correct if you guessed in all of them is approx 0.

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