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ryzh [129]
2 years ago
15

Suppose that 50% of all young adults prefer McDonald's to Burger King when asked to state a preference. A group of 12 young adul

ts were randomly selected and their preferences recorded. (Round your answers to three decimal places.)
(a) What is the probability that more than 7 preferred McDonald's?

(b) What is the probability that between 3 and 7 (inclusive) preferred McDonald's?

(c) What is the probability that between 3 and 7 (inclusive) preferred Burger King?
Mathematics
1 answer:
ddd [48]2 years ago
7 0

Answer:

a) 0.194 = 19.4% probability that more than 7 preferred McDonald's

b) 0.787 = 78.7% probability that between 3 and 7 (inclusive) preferred McDonald's

c) 0.787 = 78.7% probability that between 3 and 7 (inclusive) preferred Burger King

Step-by-step explanation:

For each young adult, there are only two possible outcomes. Either they prefer McDonalds, or they prefer burger king. The probability of an adult prefering McDonalds is independent from other adults. 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} = \frac{n!}{x!(n-x)!}

And p is the probability of X happening.

50% of all young adults prefer McDonald's to Burger King when asked to state a preference.

This means that p = 0.5

12 young adults were randomly selected

This means that n = 12

(a) What is the probability that more than 7 preferred McDonald's?

P(X > 7) = P(X = 8) + P(X = 9) + P(X = 10) + P(X = 11) + P(X = 12)

In which

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

P(X = 8) = C_{12,8}.(0.5)^{8}.(0.5)^{4} = 0.121

P(X = 9) = C_{12,9}.(0.5)^{9}.(0.5)^{3} = 0.054

P(X = 10) = C_{12,10}.(0.5)^{10}.(0.5)^{2} = 0.016

P(X = 11) = C_{12,11}.(0.5)^{11}.(0.5)^{1} = 0.003

P(X = 12) = C_{12,12}.(0.5)^{12}.(0.5)^{0} = 0.000

P(X > 7) = P(X = 8) + P(X = 9) + P(X = 10) + P(X = 11) + P(X = 12) = 0.121 + 0.054 + 0.016 + 0.003 + 0.000 = 0.194

0.194 = 19.4% probability that more than 7 preferred McDonald's

(b) What is the probability that between 3 and 7 (inclusive) preferred McDonald's?

P(3 \leq X \leq 7) = P(X = 3) + P(X = 4) + P(X = 5) + P(X = 6) + P(X = 7)

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

P(X = 3) = C_{12,3}.(0.5)^{3}.(0.5)^{9} = 0.054

P(X = 4) = C_{12,4}.(0.5)^{4}.(0.5)^{8} = 0.121

P(X = 5) = C_{12,5}.(0.5)^{5}.(0.5)^{7} = 0.193

P(X = 6) = C_{12,6}.(0.5)^{6}.(0.5)^{6} = 0.226

P(X = 7) = C_{12,7}.(0.5)^{7}.(0.5)^{5} = 0.193

P(3 \leq X \leq 7) = P(X = 3) + P(X = 4) + P(X = 5) + P(X = 6) + P(X = 7) = 0.054 + 0.121 + 0.193 + 0.226 + 0.193 = 0.787

0.787 = 78.7% probability that between 3 and 7 (inclusive) preferred McDonald's

(c) What is the probability that between 3 and 7 (inclusive) preferred Burger King?

Since p = 1-p = 0.5, this is the same as b) above.

So

0.787 = 78.7% probability that between 3 and 7 (inclusive) preferred Burger King

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Answer: A. divided the difference of the two quantities by the sum of the two quantities.

===================================================

Explanation:

The difference of the quantities is 20-15 = 5

The sum of the quantities is 20+15 = 35

Dividing those results leads to 5/35 = 0.142857 which rounds to 0.1429

That converts to 14.29%

This is likely the path Adam took. This path is incorrect. The correct steps are shown below

---------------------

Difference = 20-15 = 5

Divide the difference over the original quantity

5/20 = 1/4 = 0.25 = 25%

We have a 25% decrease because the new quantity (15) is smaller than the old quantity (20)

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Here's another way to approach the problem

A = old value = 20

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C = -0.25*100%

C = -25%

The negative C value means we have a negative percent change, ie we have a percent decrease. So this is another way to get a 25% decrease.

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