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The percent change is the increase or decrease in the value of a quantity. If the new value is larger than the original value then it is a percent increase and if the change in value is lesser than the original value it is called percentage decrease.

For example, if a person has 25 dollars and he gets 3 more dollars and now has 28 dollars, its percentage increase is calculated as shown:

$\begin{array}{l}\text{Increase}=28-25=3\\ \%\text{change=r,then}\\ \frac{3}{25}=\frac{r}{100}\\ r=\frac{3}{25}×100\\ =12\%\end{array}$

Since the new amount is larger than the original amount, there is a percent of the increase.

We are given that

$\begin{array}{l}\text{Original}:9.8\\ \text{New}:12.1\end{array}$

This is a percent of increase because the new amount is less than the original.

We find the amount of change. And calculate the percentage change as follows:

$\begin{array}{l}\text{Increase}=12.1-9.8=2.3\\ \%\text{change=r,then}\end{array}$

$\begin{array}{l}\frac{2.3}{9.8}=\frac{r}{100}\\ r=\frac{2.3}{9.8}×100\end{array}$

$\begin{array}{l}\text{r=\%change=0.2346}×100\\ \text{\%change=23.46}\\ ≈\text{23\%}\end{array}$

Rounding the answer off to the nearest whole number, the percentage change is 23%