To find the percentage increase in the number of guests from the first party to the second party, we can use the following formula for percentage increase:
\[ \text{Percentage Increase} = \left( \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \right) \times 100 \]
In this case:
- The Old Value (guests at the first party) = 25
- The New Value (guests at the second party) = 28
Now, plugging these values into the formula:
\[ \text{Percentage Increase} = \left( \frac{28 - 25}{25} \right) \times 100 \]
Calculating the difference:
\[ 28 - 25 = 3 \]
Now, substituting back into the equation:
\[ \text{Percentage Increase} = \left( \frac{3}{25} \right) \times 100 \]
Calculating the fraction:
\[ \frac{3}{25} = 0.12 \]
Now, multiply by 100 to find the percentage:
\[ 0.12 \times 100 = 12 \]
Thus, the percentage increase of the number of guests from the first party to the second party is:
\[ \boxed{12} \]