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?)