Function questions focus on mathematical functions, expressions of the mathematical relationship between two or more variables. Function questions are closely related to algebra, because all algebraic equations are relationships between variables.
According to the official Praxis Core Math Study Companion, 17 of the 56 questions found in Praxis Core Math fall under the category of Algebra and Functions. Questions about solutions to algebra equations make up the bulk of this category. But there will also be several function questions.
There are two types of function questions on Praxis Core Math. There are problems where you need to build a function. In functionbuilding questions, testtakers must come up with the correct algebraic expression for the relationship between two variables, based on the information given.
Then there are problems where you need to interpret a function. In these problems, you must look at a stated function and interpret what the function means, in terms of the relationship between the variables and the possible numerical results of the function, if it’s an algebraic expression.
Function interpretation practice question 1

J = 4K
K = 1/2L – 6

Given that both of the above expressions are true, which of the following statements describes the relationship between J and L?

A) J is 3 less than 6 times L

B) J is 4 less than 18 times L

C) J is 12 less than 1/2 times L

D) J is 24 less than 3 times L

E) J is 24 less than 2 times L
Function building practice question

2a + 7s

The expression above represents the total amount of profit, in dollars, made by selling a bags of apples and s rolls of sushi. On the day that these bags of apples and rolls of sushi were sold, a neighborhood supermarket made $2978 in profit from its combined sales of bags of apples and sushi rolls. The amount of profit earned just from selling bags of apples is what percentage of the total profit?

A) s/2978

B) 7s/2978

C) a/2978

D) 2a/2978

E) (2a + 7s)/2978
Answer Key:

1) E

2) D
Answer Explanations:
For the function interpretation problem, the two expressions can be joined into the algebraic expression of the correct answer through the following steps:

1) J = 4K, K = 1/2L – 6

2) J = 4 (1/2L – 6)

3) J = 2L – 24
Step 3 can also be described as J being 24 less than 2 times L, as seen in the answer choice (E).
For the function building problem, 2a is the variable for all profits from selling bags of apples, while 2978 is the variable for profit overall. So the correct answer needs to be a proportion of 2a and only 2a over the figure for total daily profit.
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