# Math

Published on January 21, 2008

Author: Carmela

Source: authorstream.com

Newspaper math:  Newspaper math Taking the numb out of numbers by Joe Grimm Detroit Free Press “Well, if I called the wrong number, why did you answer the phone?”:  “Well, if I called the wrong number, why did you answer the phone?” -- James Thurber Crunch or be crunched (don’t just sit there):  Crunch or be crunched (don’t just sit there) Consistency Context Completeness Care Conversions Consistency:  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 four sons: John Jr., George, Mark and Williams, and a daughter, Berry Lords. Context (know your numbers):  Context (know your numbers) Detroit population Michigan population U.S. population Comerica Park Ford annual earnings State budget Federal spending, 2000 1 million 9 million 275 million \$200-\$300 million \$7 billion \$35 billion \$1.7 trillion Context II: Make it meaningful:  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 ...:  Thrill of a trill ... Say you had the chance to blow about \$2 trillion. You could: Buy 26,317,520 Jaguar XK8 convertibles -- nearly three for everyone in Michigan. Pay off credit card debt for EVERYONE in the United States -- four times! Give \$7,272 to each of the 275 million people in the United States. Completeness (Raw numbers AND processed):  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:  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:  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 Joes Jo: 45; Joe: 40; Bill, 11; Peg & Pete, 7:  Meet the average Joes Jo: 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:  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:  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:  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):  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:  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:  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:  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:  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:  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?)

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