Question

Question 21

Consider the information provided in question 20. What is the probability that the sample mean is at least 67.5?

(1) 2.5
(2) 0.9938
(3) 0.0062
(4) -2.5
(5) None of the above

Answer 1

2)0.9938

P(X$\geq$ 67.5)

Mean=70, sd=6, sample size =36

$Z=\frac {(X-\mu) *\sqrt n} {SD}$

$Z=\frac{(67.5-70)*\sqrt{36}}{6}$

=-2.5

$\Phi(2.5)$

The value is 0.9938 from the z-tables. The answer is (2) 0.9938.