Busy. Please wait.
Log in with Clever

show password
Forgot Password?

Don't have an account?  Sign up 
Sign up using Clever

Username is available taken
show password

Make sure to remember your password. If you forget it there is no way for StudyStack to send you a reset link. You would need to create a new account.
Your email address is only used to allow you to reset your password. See our Privacy Policy and Terms of Service.

Already a StudyStack user? Log In

Reset Password
Enter the associated with your account, and we'll email you a link to reset your password.
Didn't know it?
click below
Knew it?
click below
Don't Know
Remaining cards (0)
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.

  Normal Size     Small Size show me how

Examples for Ch 7

Elementary Statistics

If the scores for a test have a mean of 100 and a standard deviation of 15, find the percentage of scores that will fall below 112. X= 112, μ= 100, σ= 15; z=(X-μ)/σ =(112-100)/15 = 12/15 = 0.8; area = .7881, 78.81% of the scores will fall below 112.
Each month, an American household generates an average of 28 pounds of newspaper for garbage or recycling. Assume the standard deviation is 2 pounds. Find the propility of its generating between 27 and 31 pounds per month. X₁= 27, X₂=31, μ= 28, σ= 2; z₁=(X₁-μ)/σ =(27-28)/2 = 3/2 = -0.5; z₂=(X₂-μ)/σ =(31-28)/2 = 1.5; area = .6247; There a 62.47% propability that a household will generate between 27 and 31 pounds of newspapers.
The average time it takes to respond to an emergency call is 25 minutes with a standard deviation of 4.5 minutes. If 80 calls are randomly selected, approximately how many will be respond to in less than 15 minutes? X= 15, μ= 25, σ= 4.5; z=(X-μ)/σ =(15-25)/4.5 = -2.22; area = .0132; n*area = 80(.0132)=1.056; Therefore, approximately one call will be responded to in under 15 minutes.
In order to qualify for a police academy, candidates must scorein the top 10% on a general abilities test. The test has a mean of 200 and a standard deviation of 20. Find the lowest possible score to qualify. 10%= .1= .1000= area; 1-area= 1-.1000= .9000; z=1.28; X= ?, μ= 200, σ= 20; z=(X-μ)/σ; 1.28= (X-200)/20; X = 226; A score of 226 is the cutoff.
The average age of a vehicle registered in the United States is 8 years, or 96 months. Standard deviation is 16 months. If a sample of 36 vehicles is selected, find the propability that the mean of their age is between 90 and 100 months. ¯X₁=90, ¯X₂=100, μ= 96, σ= 16, n=36; z=(¯X- μ)/(σ/√n); z₁=(90-96)/(16/√36)=-2.25; z₂=(100-96)/(16/√36)=1.50; area = 0.921; The propability of obtaining a sample mean between 90 and 100 months is 92.1%.
If a baseball player's batting average is 0.320 (32%), find the propability that the player will get at most 26 hits in 100 times at bat. X= 26, p=0.32, q=1-p=1-.32=.68, n=100; μ=np=(100)(.32)=32; σ=√npq= √(100)(.32)(.68)=4.66; P(X≤26), P(X<26+.5)=P(X<26.5); z=(X-μ)/σ = (26.5-32)/4.66=-1.18; area = .1190 or 11.9%.
q= Make sure p is in decimals: 1-p = q
Find the area under the normal distribution curve between z= 0 and z=2.34. Area = .4904
Find the area right of z=1.11. Area for z=1.11 is .8665; 1-.8665= .1335 or 11.35%.
Each month, an American household generates an average of 28 pounds of newspaper for garbage or recycling. Assume the standard deviation is 2 pounds. Find the propility of its generating more than 30.2 pounds per month. X= 30.2, μ= 28, σ= 2; z=(X-μ)/σ =(30.2-28)/2 = 2.2/2 = 1.1; area = .1357; There a 13.57% propability that a household will generate more than 30.2 pounds of newspapers.
Created by: dengler
Popular Math sets




Use these flashcards to help memorize information. Look at the large card and try to recall what is on the other side. Then click the card to flip it. If you knew the answer, click the green Know box. Otherwise, click the red Don't know box.

When you've placed seven or more cards in the Don't know box, click "retry" to try those cards again.

If you've accidentally put the card in the wrong box, just click on the card to take it out of the box.

You can also use your keyboard to move the cards as follows:

If you are logged in to your account, this website will remember which cards you know and don't know so that they are in the same box the next time you log in.

When you need a break, try one of the other activities listed below the flashcards like Matching, Snowman, or Hungry Bug. Although it may feel like you're playing a game, your brain is still making more connections with the information to help you out.

To see how well you know the information, try the Quiz or Test activity.

Pass complete!
"Know" box contains:
Time elapsed:
restart all cards