Final answer:
There were 40 cakes in total at the holiday fair, and 12 of them were chocolate.
Step-by-step explanation:
To find out how many cakes were chocolate, we first need to determine the total number of cakes at the holiday fair. Out of the 40 parents that volunteered, 10 of them brought two cakes, so we have 40 - 10 = 30 parents who brought one cake each. Therefore, there are 30 + 10 = 40 cakes in total at the holiday fair.
Since 30% of the cakes were chocolate, we can calculate the number of chocolate cakes by multiplying the total number of cakes by the percentage. So, 40 * 0.30 = 12 cakes were chocolate at the holiday fair.