The expression for percentage is
[tex]Percentage=\frac{\text{Amount whose percentage has to be calculated}}{Total\text{ amount}}\times100[/tex]Here out of 300 people, 90 people have allergic
[tex]\begin{gathered} \text{Percentage =}\frac{Number\text{ of people have mild allergic}}{Total\text{ number of people used Shampoo}}\times100 \\ \text{Percentage}=\frac{90}{300}\times100 \\ \text{Percentage}=\frac{90}{3} \\ \text{Percentage}=30 \end{gathered}[/tex]The percentage of peoplw who have mild allegric is 30%
Answer : 30%
