Given X~N(21,4)

Question

(a)Find the z-score for 

(b)Would x= 10 be considered usual, unusual, or very unusual?

Answer 1

can only do b).

z = (x - mean) / std dev = (10 -21)/4 = -2.75.

P(z < -2.75) = 0.0030, which makes it a very low probability and very unusual.