Intro to Standard Deviation

The z-score represents.....

• the amount of standard deviations a data value is above or below the mean.

• the percentile the data value is above or below the mean.

• the amount of standard deviations a data value is above or below the median.

• the percent the data value is above or below the mean.

Find the area of the shaded region. 

• 0.16

• 0.84

• 0.68

• 0.34

What's the probability of the gray area? (Mean = 55, Standard dev = 2.5)

• 0.8185

• 0.8413

• 0.8641

• 0.8389

The mean life of a tire is 30,000 km. The standard deviation is 2000 km.

Then, 68% of all tires will have a life between ___________ km and __________ km.

•  28,000 km and 32,000 km.

• 24,000 km and 34,000 km.

• 26,000 km and 34,000 km.

• 27,000 km and 31,000 km.

The shelf life of a particular dairy product is normally distributed with a mean of 12 days and a standard deviation of 3 days.

About what percent of the products last between 12 and 15 days?

• 68%

• 34%

• 16%

• 2.5%

Between what two standard deviations of a normal distribution contain 68% of the data?

• one below and one above

• two below and two above

• two below and zero

• zero and two above

The mean GPA of students in a course at UCDavis is 3.2 with a standard deviation of 0.3. What percent of students in the course have a GPA between  2.9 and 3.8?

• 81.5%

• 47.5%

• 68%

• 95%

The 40 yards sprint times for a soccer team are found to be normally distributed with a mean of 5.2 seconds and a standard deviation of 0.3 seconds.  What is the z-score for a player who runs a time of 5.6 seconds?

• -1.33

• 1.33

• 0.88

• 1.02

μ = 70 , σ = 8 , X = 50 . Find z score

• 2.5

• -2.5

• 5.2

• -5.2

The monthly phone bills in a city are normally distributed with a mean of 30$ and a standard deviation of 12$. Find the x-value that correspond to z-scores of 3.17. 

• $1.80 

• $68.04

• $32.76