# math

posted by susan

A true-false test consists of 15 items.

(b) What is the probability that Chris gets 80% or more for the test?
(c) If it is a 25 item true-false test, would you think it is easier or more difficulty for Chris to get 80% or more? (Hint: please calculate the corresponding probability that Chris gets 80% or more for the test, and compare your results with the one obtained in (b) to answer this question.)

b) he must get 13 right or 14 right or 15 right
= C(15,13)(1/2)^13 (1/2)^2 + C(15,14)(1/2)^14(1/2) + C(15,15) (1/2)^15
= 0.01922%

c) he must get 23 right or 24 right or 25 right
= C(25,23)(1/2)^23 (1/2)^2 + C(25,24)(1/2)^24(1/2) + C(25,25) (1/2)^25
= 5.36441803e-0.5

1. Reiny

The assumption would be that he would be randomly guessing at the answer.

Since 12/15 = .8, why did you not include the probability of getting 12 correct out of the 15 ?
Try adding that to your other cases.

For b) wouldn't getting 20 out of 25 correct yield 80% ?
Same for 21 and 22
So you have a few more cases to include

2. lol

maybe speak to your tutor if you're having issues. very easy to get done for plagiarism for this when it shows up as the first result on google. QUT is coming for you

## Similar Questions

1. ### Math

Jack is taking a four-item true-false test. He has no knowledge about the subject of the test and decided to flip a coin to answer the items. What is the probability that he receives a perfect score?
2. ### MATH Prob.

Jack is taking a four-item trueâ€“false test. He has no knowledge about the subject of the test and decides to flip a coin to answer the items. What is the probability that he receives a perfect score?
3. ### math

Could someone please tell me if I am on track with my answer?
4. ### statistics

a test consists of true/false questions .to pass the test a student must answer at least 6questions correctly .if a student guesses on each question,what is the probability that the student will pass the test
5. ### MATH 157

Can anyone please help me understand these math problems. #4. How many three-symbol codes (letter-number-number)can be made from the letters S, P, Y, and two-digits from the set of (0, 1, 2,..., 9) without repetition?
6. ### math

the question is: If you know that 4 of the 10 items on a true-false test are false, how many different ways could you select 4 items to mark as being false?
7. ### tats

No(Did not lie) Yes(lied) positive test result 15(false positive) 42(true positive) negative test result 32(true negative) 9 (false negative) Refer to table and assume that one of the 98 test subjects is randomly selected. Find the …
8. ### Math

A true-false test consists of 10 items. What is the probability that Chris gets 80% or more for the test?
9. ### math

A true-false test consists of 15 items. (a) If Chris does not study at all and guesses each and every item in the test, describe the probability model for the number of correct guesses. (b) What is the probability that Chris gets 80% …
10. ### math

A true-false test consists of 15 items. (a) If Chris does not study at all and guesses each and every item in the test, describe the probability model for the number of correct guesses. each individual question has a probability of …

More Similar Questions