To calculate the percent of people who had a mild allergic reaction, we can set up the proportion you mentioned:
\[ \frac{42}{7000} = \frac{p}{100} \]
Here, \( p \) represents the percentage of people who experienced a mild allergic reaction. To find \( p \), we can cross-multiply and solve for \( p \):
\[ 42 \times 100 = 7000 \times p \]
This simplifies to:
\[ 4200 = 7000p \]
Next, divide both sides by 7000 to isolate \( p \):
\[ p = \frac{4200}{7000} \]
Calculating this gives:
\[ p = 0.6 \]
To find the percentage, we multiply by 100:
\[ p = 0.6 \times 100 = 60% \]
Thus, \( 60% \) of the people had a mild allergic reaction.