Answer:
28. Correctly used
30. Incorrectly used
Explanation:
You want to know if the word "function" is correctly used in the following cases:
28. The sales tax on a purchased item in a given state is a function of the selling price.
30. A function pairs each chaperone on a school trip with 10 students.
28. Sales tax
There is exactly one value of sales tax associated with any given selling price. This means the ordered pair (selling price, sales tax) will be unique for any given selling price. Hence, the relation between selling price and sales tax is a function. The word function is used correctly in describing this relation.
29. Chaperones
There are 10 different students associated with any given chaperone. This means there will be multiple (chaperone, student) ordered pairs for any given chaperone: (c1, s1), (c1, s2), ..., (c1, s10), (c2, s11), (c2, s12), ..., (c2, s20), .... The relation between chaperones and students is not a function. The word function is used incorrectly in describing this relation.