Hello I am a College student trying get through my elmentry concepts class. I am also working with the middle and elementry school student with their work. I was given a few problems to work on and i am having a hard time explaining them to students. DO you think you can help with a coupld of these questions! Thanks!

What is wrong with each:

  1. Since there are fifty states, the probability of being born in Wyoming is 1/50.

  2. The probability that a person smokes is .45 and that he drinks is .54; therefore the probability that a person smokes or drinks is .99

  3. the proability that a certain candidate for president of the US. will win is 3/5, and that she will lose is 1/4.

  4. On June 1, 1993, the average age of 33 employees at Acme Cement was 47 years. One June 1, 1994 three of the staff retire at the ages of 65, 58, and 62. They were replaced by four employees aged 24, 31, 26, and 28. What was the average age of employees on June 1, 1994?

  5. And "If a fair die is rolled twice, what is the proability of rolling a pair of f's?" well a student responded one third becuase on sixth plus one sixth is one third. How would i respond to his response.

Thanks again!


Here are a few ideas

  1. Suppose that you had a birth certificate for everyone born in the US. You could sort this list into 50 piles, one for each state. The New York pile and the California pile would be much larger that the Wyoming pile. If you were to select one birth certificate from the unsorted list you would be much more likely to get someone born in New York or California than Wyoming.

  2. Suppose that you went into a room with 100 people and put a "smoker" button on the 45 people who are smokers. Suppose that you then put a "drinker" button on the 54 people who are drinkers. How many buttons in total have you used? 99
    How many people have two buttons? I don't know.
    How many people have a button? I don't know.
    The people who have a button are the people who are either smokers or drinkers. There are most likely less than 99 since some people are both smokers and drinkers. If you just count buttons to get 99 you are counting the people who are smokers and drinkers twice.

For problem 4 to find the average on June 1, 1993 first you found the total of the ages of the 33 employees. This total was divided by 33 to get an average of 47. Thus the total of the ages was 33 x 47 = 1551. To find the average on June 1, 1994 this total has changed. You need to remove the people who have retired (subtract their ages) and include the new employees (add their ages). Then divide to find the average.

I hope this helps,
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