Nevertheless, we have kids needing help with such glorious concepts as decimals, fractions, and percents (not to mention slope and matrices...eek). So I wanted to share with y'all my favorite way of teaching percent increase or decrease.
The Nitty Gritty Math Facts (in case you need a crash course):
Basically a percent is just a fraction comparison. The fraction represents some part compared to the whole number which is equal to a number (the percent) over 100. We always consider the percent out of 100. That's what percent means-- "per 100."
If Bigbad has 5 female cousins out of 12 cousins total, our fraction would be 5/12. So what percentage of female cousins does he have?
|If you are a visual person and need the steps written out. I usually have to do the visualization first. So by cross multiplying I get 12p = 500. Divide both sides by 12 = 41.67%. But below is the snappy fast formula...|
Our math problem would look like this (5/12)*100=41.667. 41.667% of his cousins are female.
Great, let's move on to percent increase and decrease. How about an explanation?
Percent increase and percent decrease are measures of percent change, which is the extent to which something gains or loses value. Percent changes are useful to help people understand changes in a value over time. (Source: Math Goodies)To get percentage increase/decrease, our fraction comparison is the difference between the original number and the new number. Divide the absolute value (basically ignore any negative signs) of that difference by the original number and multiply by 100.
So if we're trying to find out the percentage increase for hybrid vehicles in our neighborhood, we'd need the original number of hybrid cars (4) and the new number of hybrid cars (9).
I4-9I/4*100=125. 125% increase. Which makes sense because a 100% increase would be 4 more vehicles (making the total 8), but we had one more than that.
For more practice, grab the Black Friday sales flyers. If you have the holiday price and original price, you can discover the percent decrease.
Here's the formula again if you are a visual person:
Find out the markup/markdown difference between the two prices. $150-$89= $61. 61/150 *100 = a 40% decrease from the original price.
Find out how much a household staple cost in years past. How much was a gallon of gas the year you were born or how much did it cost your grandparents to mail a letter? How much is it now? Use the percent increase/decrease calculator to check your work.
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