Post on 14-Dec-2014
description
transcript
Newspaper math
Taking the numb out of numbers
by Joe Grimm
Michigan State University
“Well, if I called the wrong number,
why did you answer the phone?”
-- James Thurber
Crunch or be crunched(don’t just sit there)
• Consistency
• Context
• Completeness
• Care
• Conversions
Consistency
John Smith, who survived World War II and the Korean conflict, died of an accidental gunshot wound Thursday. He was 67. Smith was survived by five sons: John Jr., George, Mark and Williams, and a daughter, Berry Lords.
Context (know your numbers)
Detroit population
Michigan population
U.S. population
Comerica Park
Ford pre-tax earning
Michigan budget, 2014
U.S. spending budget ’14
700,000
10 million
313 million
$200-$300 million
$8.6 billion
$35 billion
$3.77 trillion
Context II: Make it meaningful
“The value of (Gates’) stock … reached an incredible $81.4 billion. To put that in perspective: That’s 209,357,326 14-ounce tins of Beluga caviar or 513 Boeing 747s, or nearly the gross domestic product of Israel. In other words, it’s a lot more money than most people can fathom.”
-- USA Today
Thrill of a trill ...
Say you had the chance to blow about $2 trillion. You could:
• Buy 43,478,260 Jaguar XF convertibles – more than four for everyone in Michigan.
• Pay off credit card debt for EVERYONE in the United States -- four times!
• Give $6,389 to each of the 313 million people in the United States.
Completeness(Raw numbers AND processed)
• A 7 percent increase in MSU’s budget
• Putting 1,000 more police on U.S. streets
• One million workers wear headphones
• Sanitation workers get a 10 percent raise
• The hospital cut 200 workers
• Auto Show attendance is up 12 percent
Use care
• Does it make sense?
• Is it million or billion?
• Is that an increase of 2 percent, or 2 percentage points?
• Watch superlatives
• Check dates, phone numbers
Conversions
• Start by estimating – Weight of a premature baby– Boiling water– The distance from Detroit to Chicago
• Then use conversion tables and calculators
Meet the average JoesJo: 45; Joe: 40; Bill, 11; Peg & Pete, 7
• Average age: 22
• Median age: 11
• Mode: 7
What does this imply about the average wage at Microsoft?
Percentage
• Percent simply means “per hundred.”• That means a percent can be expressed as
anything divided by a hundred.
• We generally don’t have trouble with a percentage: “27 percent of students have tattoos.”
• The difficulty is with percent change
Percent increase
• Three numbers are under consideration:– What you start with– What you end with– The difference
• Any two will give you the third and the percentage
Let’s try one
• What is the percent increase from 50 to 75?– The difference is 25.– Divide the difference by the starting number:
25/50 = .5 = 50%
Answer: A 50 percent increase
Do some on your own(Estimate, calculate, think)
• What is the increase:
• from 100 to 200?
• From 40 to 65?
• From 2,800 to 35,000?
• From $9.47 to $12.13?
• From $1.4 million to $1.9 million?
Percentage decrease
• We still are focusing on the difference between before and after.
• We still divide the difference, or the amount of the change, by the starting number.
• The only thing that changes is we are starting with a larger number, rather than a smaller number.
Let’s try a decrease together
• What is the percent decrease from 75 to 50?– The difference is 25.– Divide the difference by the starting number:
25/75 = .33 = 33%
Answer: A 33 percent decrease
(Why wasn’t the answer 50% this time?)
This time, you know the percent
• Calculating percentage changes is easy. Simply multiply the beginning number by the percentage.
• Remember, NO increase would be times 1, so a 20 percent increase would mean you multiply the starting number by 1.20.
Try some increases
• What would a 20 percent increase do to a $800 paycheck?
• A city with a population of 70,000 grows by 7 percent
• A state budget of $185,000 goes up by 30 percent.
Now, try some decreases
• What would a 20 percent decrease do to a $800 paycheck?
• A city with a population of 70,000 shrinks by 7 percent
• A state budget of $185,000 goes down by 30 percent.
(What about the numbers this time? Why?)