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Marianna [84]
3 years ago
14

Here is a simple probability model for multiple-choice tests. Suppose that each student has probability p of correctly answering

a question chosen at random from a universe of possible questions. (A strong student has a higher p than a weak student.) The correctness of answers to different questions are independent. Jodi is a good student for whom p = 0.85.(a) Use the normal approximation to find the probability that Jodi scores 78% or lower on a 100-question test.(b) If the test contains 250 questions, what is the probability that Jodi will score 78% or lower?
Mathematics
1 answer:
Alla [95]3 years ago
6 0

Answer:

a) The probability that Jodi scores 78% or lower on a 100-question test is 4%.

b) The probability that Jodi scores 78% or lower on a 250-question test is 0.023%.

Step-by-step explanation:

a) To approximate this distribution we have to calculate the mean and the standard distribution.

The mean is the proportion p=0.85.

The standard deviation can be calculates as:

\sigma=\sqrt{\frac{p(1-p)}{n} }= \sqrt{\frac{0.85*(1-0.85)}{100} }=0.04

To calculate the probability that Jodi scores 78% or less on a 100-question test, we first calculate the z-value:

z=\frac{p-p_0}{\sigma} =\frac{0.78-0.85}{0.04} =-1.75

The probability for this value of z is

P(x

The probability that Jodi scores 78% or lower on a 100-question test is 4%.

b) In this case, the number of questions is 250, so the standard deviation needs to be calculated again:

\sigma=\sqrt{\frac{p(1-p)}{n} }= \sqrt{\frac{0.85*(1-0.85)}{250} }=0.02

To calculate the probability that Jodi scores 78% or less on a 250-question test, we first calculate the z-value:

z=\frac{p-p_0}{\sigma} =\frac{0.78-0.85}{0.02} =-3.5

The probability for this value of z is

P(x

The probability that Jodi scores 78% or lower on a 250-question test is 0.023%.

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