I need help for number 49

Mathematics

1 answer:

Dmitry_Shevchenko [17]3 years ago

8 0

I'm thinking it's B for that question

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Question 8. I need help !!

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Suppose you take a 30-question, multiple-choice test, in which each question contains 4 choices: A, B, C, and D. If you randomly

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Answer:

(a) The probability you pass the exam is 0.0000501.

(b) The expected number of correct guesses is 7.5.

(c) The standard deviation is 2.372.

Step-by-step explanation:

We are given that you take a 30-question, multiple-choice test, in which each question contains 4 choices: A, B, C, and D. And you randomly guess on all 30 questions.

Since there is an assumption of only 1 correct choice out of 4 which means the above situation can be represented through binomial distribution;

$P(X =x) = \binom{n}{r}\times p^{r}\times (1-p)^{n-r} ; x = 0,1,2,3,......$

where, n = number of trials (samples) taken = 30

r = number of success = at least 60%

p = probbaility of success which in our question is the probability

of a correct answer, i.e; p = $\frac{1}{4}$ = 0.25

Let X = Number of questions that are correct

So, X ~ Binom(n = 30 , p = 0.25)

(a) The probability you pass the exam is given by = P(X $\geq$ 18)

Because 60% of 30 = 18

P(X $\geq$ 18) = P(X = 18) + P(X = 19) +...........+ P(X = 29) + P(X = 30)

= $\binom{30}{18}\times 0.25^{18}\times (1-0.25)^{30-18} + \binom{30}{19}\times 0.25^{19}\times (1-0.25)^{30-19} +.......+ \binom{30}{29}\times 0.25^{29}\times (1-0.25)^{30-29} + \binom{30}{30}\times 0.25^{30}\times (1-0.25)^{30-30}$