In a recent year the magnitudes​ (Richter scale) of​ 10,594 earthquakes were recorded. The mean is 1.224 and the standard deviation is 0.56. Consider the magnitudes that are unusual.

Question

In a recent year the magnitudes​ (Richter scale) of​ 10,594 earthquakes were recorded. The mean is 1.224 and the standard deviation is 0.56. Consider the magnitudes that are unusual. What are the magnitudes that separate the unusual magnitudes from those that are​ usual? ​(Consider a value to be unusual if its z score is less than −2 or greater than​ 2.)

QUESTION: The lower bound earthquake magnitude is _______.

​(Type an integer or a​ decimal.)

Answer 1

z = (x - mean)/SD

2 = (x - 1.224)/0.56

x = 2.344

-2 = (x - 1.224)/0.56

x = 0.104 ( lower bound)