The Percent Change Equation

When you go shopping on Black Friday and Cyber Monday, you’ll probably see coupons like “$50\%$ off select items!” or “$25\%$ off your entire order!” You might find yourself wondering, what do these mean exactly?

The coupons in the GIF above are examples of percent change. Any time we have a number that changes, we can use the percent change formula below to determine how big that change was.

The following fraction gives us what portion of the initial value changed in decimal form:

We know we need to multiply decimals by $100$ to change them to percents, so the percent change formula is equal to:

Check out our Percent Change Calculator below for examples of different ways we can use the percent change formula to solve for percent change, final value, and initial value:

Percent Change in Voter Turnout

Percent increase and decrease tell us how things change, and in the real world, they are often used to determine the effects of certain policies. For example, voting is an important part of any democracy. Even if you can’t vote, the results of elections can affect how much medicine costs, how much you get paid, and even what classes your school teaches.

Because voting is so powerful sometimes, politicians who fear losing power create unfair policies and practices that prevent certain people from voting. This is often referred to as voter suppression. Using percent increase and decrease can help us determine the effects of voter suppression.

Let's look at this data from Michael McDonald, a political science professor at the University of Florida. We’ve rounded the numbers a little, but the table below shows the number of Black voters (in thousands) that voted early during the $2012$ and $2016$ presidential elections in four different states:

Which of these states had a decrease in early voter turnout between $2012$ and $2016$?

That’s exactly right! Of these four states, North Carolina was the only one whose early voter turnout decreased.

In $2013$, North Carolina passed a Voter ID law that required stricter voter ID, removed certain voting locations, and made early voting periods shorter. The law was struck down just before the $2016$ presidential election, but many suspected it would still affect voter turnout.

To see the effects of the Voter ID Law, let’s calculate the percent change for the number of early Black voters in North Carolina:

Amazing job! Our initial number was $754$, and our final was $688$. Now we just need to perform the calculations. Click the 🏆 when you’re ready to reveal the answer

The number of Black voters who voted during the early voting period in North Carolina decreased by $\bold{8.7\%}$ between the $2012$ and $2016$ elections. According to the ACLU, in North Carolina, about $70\%$ of Black voters voted early in $2008$ and $2012$, so the $2013$ law would have had the largest effect on Black voters in the state.

Looking at the table, we can see that the number of Black voters who voted early increased in the other three states between $2012$ and $2016$. Since Florida, Louisiana, and Georgia did not change their early voting laws during this time, this data might lead us to believe that the $2013$ law led to voter suppression in North Carolina.