Answer: -3
Work Shown:
z = (x - mu)/sigma
z = (46 - 70)/8
z = -24/8
z = -3
Explanation: This z score is negative to indicate we're below the mean. Specifically, this value is exactly 3 standard deviations below the mean.
Note the (x-mu) portion tells us the gap from x to mu. Dividing by the standard deviation sigma will place this distance in terms of standard deviation units. This helps connect to the fact that the standard deviation tells us how spread out the data set is.
