Question

Suppose that four students scores are selected randomly from the exam that has a st dev of 1.8 and a mean of 70 what is the probability that the average score for those four selected exams is greater than 73?

Answer 1

You're working with the xbar distribution (distribution of sample means)

\(\Large \bar{x}\) = xbar = 73
\(\Large \mu\)= mu = 70
\(\Large \sigma\)= sigma = 1.8
n = 4


Test Statistic
\[\Large z = \frac{\bar{x} - \mu}{\frac{\sigma}{\sqrt{n}}}\]

\[\Large z = \frac{73-70}{\frac{1.8}{\sqrt{4}}}\]

\[\Large z = ??\]

Tell me what you get

Answer 2

let me know if you get stuck @Tomfoolery1

Answer 3

3.3333? i hope thats right

Answer 4

yep that's the correct z score

now use either a calculator or a table to compute P(Z > 3.33)

Answer 5

The table should be in the back of your text book

Answer 6

0.999566 this is what i got

Answer 7

http://www.stat.ufl.edu/~athienit/Tables/Ztable.pdf

using that table

P(Z < 3.33) = 0.9996

so

P(Z > 3.33) = 1 - P(Z < 3.33)
P(Z > 3.33) = 1 - 0.9996
P(Z > 3.33) = 0.0004