To calculate the inflation rate from 2018 to 2019 using the Consumer Price Index (CPI), you can use the following formula:
\[ \text{Inflation Rate} = \left( \frac{\text{CPI in 2019} - \text{CPI in 2018}}{\text{CPI in 2018}} \right) \times 100 \]
Plugging in the values:
\[ \text{Inflation Rate} = \left( \frac{257 - 251}{251} \right) \times 100 \]
Calculating the difference:
\[ 257 - 251 = 6 \]
Now, substituting back into the formula:
\[ \text{Inflation Rate} = \left( \frac{6}{251} \right) \times 100 \approx 2.39% \]
Rounding to the nearest tenth of a percent gives us approximately:
\[ 2.4% \]
Therefore, the correct response is:
2.4%