a company that makes hair-care products had 3000 people try a new shampoo. Of the 3000 people, 9 had a mild allergic reaction. What percent of people had a mild allergic reaction?

Answer: Hello mate!

We know that out of 3000 people, 9 had a alergic reaction.

in this case our 100% is 3000, and we want to know what percentage is equivalent to those 9 that had a mild allergic reaction.

here we can use the rule of 3, this is:

if 3000 is equivalent to 100%, then 9 is equivalent to:

(9/3000) * 100% = 0.3%