Math for Journalists

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• Math for Journalists

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The Journalism Schools budget for computer
programs jumped from 5,500 to 7,300. By what
percent did it increase?
Percent difference N/O 1 (New number/ Old
number -1) (7,300/5,500) 1.327 Subtract 1, and
you get .327
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To convert .327 to a percent, Move the decimal
two places to the right .327 32.7
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Comparing apples and oranges

• Rates (percent)
• Index numbers (CPI)
• Percentile rankings (SAT v. ACT)
• Standardized scores (standard deviation units)

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Percent is a rate per hundred

• First, convert the fraction to a decimal by
  division.
• ¾ .75
• To get a rate per hundred, multiply by 100
• .75 100 75
• Another word for rate per hundred is percent.

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Other rates

• To get a rate per thousand, multiply by 1,000.
• .75 1000 750
• To get a rate per hundred thousand, multiply by
  100,000
• .75 100,000 75,000

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Example

• A military unit of 41,000 persons had 49 suicides
  over a 10-year period. Its 10-year suicide rate
  was
• .1195 percent
• 1.195 per thousand
• 119.5 per hundred thousand
• Choose a rate that yields whole numbers

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A gallon of paint covers 400 square feet. How
many gallons to coat one side of a fence that is
7 feet high and 300 feet long?
First figure the area 7 300 2,100 square feet
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A gallon does 400 square feet. How many 400s in
2,100? 2,100/400 5.25
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The police force has 693 officers, 5 percent more
than it had before. How many did it have before?
What number when multiplied by 1.05 yields
693? Answer 693/1.05 660
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Valuation is 127,500 and tax is 1,466.25. What
is the rate per 100 valuation?
How many hundreds in 127,500? 1,275 What number
multiplied by 1,275 yields 1,466.25? Answer
1,466.25/1,275 1.15
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If algebra makes it easier
1,275 X 1,466.25 X 1.466.25/1.275 X 1.15
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The pizza problem
¾ of a pizza To divide 4 ways
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3/4 6/8 12/16 Each roommate gets 3/16 of the
pizza.
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Do order-of-magnitude checks
The coach expressed concern because .05 of his
team members failed a preliminary drug screening.
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Drug-using athletes

• 5 percent 5 out of 100 or 1 in 20
• .5 percent 5 out of 1,000 or 1 in 200
• .05 percent 5 out of 10,000 or 1 in 2,000

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RALEIGH, N.C. (AP) - American history is being
preserved at the North Carolina birthplaces of
two of the nation's early presidents, James K.
Polk (1845-49) and Andrew Johnson (1865-69).
Polk pushed an expansionist vision during his
term, adding about 500 million square miles to
the Western United States.
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Think!
The distance from New York to Los Angeles is
about 3,000 miles. A square with 3,000 miles on
each side would contain 3,000 3,000 or 9
million square miles. Therefore, the entire
continental USA could easily fit inside 9 million
square miles.
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RALEIGH, N.C. (AP) - In an Aug. 17 story about
presidential birthplaces,The Associated Press
erroneously reported the amount of territory
addedto the United States during the presidency
of James K. Polk. The correct figure is 1.2
million square miles, not 500 million square
miles.
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Anything wrong?
Average gas price likely to top 2 Fuel could
hit record as soon as this weekend
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The record is
In nominal dollars 2.05 In constant 2004
dollars 2.95
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(No Transcript)
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Broiled Filet Mignon, French Fried Potatoes,
Bread, Butter, and Beverage 2.75
Whats that in constant 2005 dollars?
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Consumer Price Index

• June 1948 24.2
• January 2005 190.7
• 24.2 2.75
• 190.7 X
• X (190.7 2.75) / 24.2

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http//www.bls.gov/cpi/home.htm

• 2.75 in 1948
• had the same buying power
• as
• 21.67 in 2005.

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How to write with numbers

• First rule no more than two numbers in a
  paragraph

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Example

• Revenue at the largest generator of electricity
  in the USA soared to 61.3 billion in 2001 from
  13.7 billion in 2000. Yet to get that much more
  revenue, the company added 5 more workers to
  27,726 and assets declined 13 to to 47.3
  billion from 54.5 billion.
• --USA Today

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How to write with numbers

• Second rule if you use two numbers in a
  paragraph, its better if they can be compared
  with each other.

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Example

• Boston had a season total of 78.1 inches of
  snow by Tuesday. Its average annual total is
  about 42 inches.
• --USA TODAY, March 2, 2005

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How to write with numbers

• Third rule dont use more significant digits
  than you need.
• If 62.34 of the public supports Bush, report it
  as 62.
• Remember polls are never accurate to fractions
  of a percentage point.

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On the other hand

• Felony theft is defined as taking goods worth 50
  or more. A shoplifter steals a sweater priced at
  49.99.
• Should the prosecutor round to 50 and file a
  felony charge?

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Writing with numbers

• Express the concept in words first.
• Then back it up with the numbers.
• Show the numbers as part of a system.

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Example
A new study finds what may seem obvious to even
casual observers Many National Football League
players are obese. --USA TODAY, March 2, 2005
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Five paragraphs later

• 56 or players qualify as obese, roughly 30 or
  more pounds over a healthy weight.
• About 26 of football players qualify as severely
  obese, and 3 are morbidly obese.

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Writing with numbers

• Choose your typical value carefully
• Mean the value each case would have if each
  case were the same (and the total was constant).
• Median value of the middle case.
• Mode the most frequent value.

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Where money is involved, the mean can be
misleading
The tax relief is for everyone who pays income
taxes and it will help our economy immediately
92 million Americans will keep, this year, an
average of almost 1,000 more of their own
money. -- George W. Bush, State of the Union
Address, 2003
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More than 80 receive less than 1,000
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Graduates of what UNC department have the highest
mean salary?

• School of medicine
• School of journalism
• School of law
• Department of geography
• School of business administration

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• (Michael Jordan majored in geography!)