Question

Precalculus: Will someone please check my answers?

For exercises 14 and 15, a set of data has a normal distribution with a mean of 120 and a standard deviation of 10.

14. Find the interval about the mean within which 90% of the data lie.

94.2-145.8
103.5-136.5<---my answer
113.68-126.32
100.4-139.6

15. Find the probability that a value selected at random from this data is between 100 and 140.

99.9%
90%
99%
95.5%<---my answer

Answer 1

Could you explain?

Answer 2

@ganeshie8

Answer 3

zscore for left tail at 5% = -1.65

\(\implies -1.65 = \dfrac{L - 120}{10} \implies L = 103.5\)

Answer 4

B is correct for #14

Answer 5

#15 is also right ! the question is just asking u to calculate 2sigma percentage which is 95.45%

Answer 6

Yay thank you! I have one more question I'm unsure about, if you don't mind?

Answer 7

sure

Answer 8

A set of 300 values has a normal distribution with a mean of 50 and a standard deviation of 5. If needed, round your answer to the tenths place.

27. Find the probability that a value selected at random from this data is between 49.5 and 50.5.

This one is not multiple choice. I got 8.0%

Answer 9

http://www.wolframalpha.com/input/?i=P%28%2849.5-50%29%2F5%3CX%3C%2850.5-50%29%2F5%29

Answer 10

^^ 8% is right !

Answer 11

Yay thanks! :)

Answer 12

good work ! yw