When an item goes on sale, or rises in price, this is often referred to as a percent decrease or increase. This isn't anything new, no new processes to learn or rules to memorize. Basically, it's just turning a fraction into a percent.
To find percents of increase or decrease, all we need to do is take the difference in amount and divide it by the original amount, just as you would to turn a fraction into a decimal. Finally multiply this by 100, just as you would to turn a decimal into a percent.
Last week gasoline was $3.29/gallon. This week it is $3.59/gallon. What is the percent increase?
The price of a dozen eggs was $2.29, but is now $2.09. What is the percent decrease?
Last year only 50 people attended the annual holiday choir concert. This year it was mandatory that everyone bring two guests, so there were 160 attendees. What is the percent increase?
In a small town in New York, the population has been slowly declining. In 1999 there were 2087 residents, and only 1560 in 2009. What is the percent decrease?
The price of a Shmintendo game system has decreased over the years. When the Shmintendo was first introduced it was $249. A few years later, a Shmintendo sold for $199. What is the percent decrease?
In the early 1900's the average life span for US citizen was 49 years. It is now 78.2 years. What is the percent increase?