Function Rules and Output

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ISEE Middle Level: Quantitative Reasoning › Function Rules and Output

Questions 1 - 10
1

A number-processing machine follows a two-step rule. First, it multiplies the input number by -3. Second, it subtracts 7 from the result. If the input number is -5, what is the final output?

-22

8

22

36

Explanation

The correct answer is 8. The function rule has two steps. Step 1: Multiply the input by -3. So, \((-5) \times(-3) = 15\). Step 2: Subtract 7 from the result. So, \(15 - 7 = 8\). The final output is 8.

2

Commission rule: $c = 3s + 10$. Find $c$ when $s = 6$.

13

16

18

28

Explanation

This question tests middle school quantitative reasoning skills, specifically using a function rule to determine output. Function rules allow us to calculate output values by substituting input values into an algebraic expression. In this question, the commission rule c = 3s + 10 is used to find commission c when sales s = 6. Choice A is correct because substituting 6 for s yields c = 3(6) + 10 = 18 + 10 = 28, demonstrating proper function application. Choice C (18) represents the common error of forgetting to add the constant term, calculating only 3(6). Choice D (16) might result from adding before multiplying, while Choice B (13) could come from various calculation errors. To help students, stress the importance of following each step carefully and checking work. Real-world contexts like commission calculations make abstract concepts more concrete and meaningful.

3

Commission rule: $c = 5s - 2$. Find $c$ when $s = 7$.

17

23

33

37

Explanation

This question tests middle school quantitative reasoning skills, specifically using a function rule to determine output. Function rules allow us to calculate output values by substituting input values into an algebraic expression. In this question, the commission rule c = 5s - 2 is used to find commission c when sales s = 7. Choice A is correct because substituting 7 for s yields c = 5(7) - 2 = 35 - 2 = 33, demonstrating proper function application. Choice C (37) might result from adding 2 instead of subtracting, while Choice D (23) could come from calculating 5(5) - 2. Choice B (17) appears to result from a calculation error. To help students, stress careful attention to operations (subtraction vs. addition) and systematic substitution. Commission problems provide real-world context that makes abstract algebra more meaningful.

4

Car distance rule: $d = 30t$. Find $d$ when $t = 4$.

34

90

120

300

Explanation

This question tests middle school quantitative reasoning skills, specifically using a function rule to determine output. Function rules allow us to calculate output values by substituting input values into an algebraic expression. In this question, the car distance rule d = 30t is used to find distance d when time t = 4. Choice A is correct because substituting 4 for t yields d = 30(4) = 120, demonstrating proper function application through simple multiplication. Choice C (90) might result from calculating 30(3), while Choice B (34) could come from adding 30 + 4. Choice D (300) appears to result from multiplying by 10 instead of 4. To help students, emphasize careful multiplication and the direct proportional relationship in this function. Distance-time problems provide intuitive context for understanding linear functions without constant terms.

5

Discount rule: $y = 10x - 5$. Find $y$ when $x = 4$.

5

25

35

45

Explanation

This question tests middle school quantitative reasoning skills, specifically using a function rule to determine output. Function rules allow us to calculate output values by substituting input values into an algebraic expression. In this question, the discount rule y = 10x - 5 is used to find the discounted price y when x = 4. Choice A is correct because substituting 4 for x yields y = 10(4) - 5 = 40 - 5 = 35, demonstrating proper function application. Choice B (45) might result from adding 5 instead of subtracting, while Choice D (25) could come from calculating 10(4) - 15. Choice C (5) appears to be an error in calculation or misunderstanding of the function. To help students, emphasize the difference between addition and subtraction in function rules. Real-world contexts like discounts help students understand practical applications of linear functions.

6

Car distance rule: $d = 40t + 5$. Find $d$ when $t = 2$.

45

80

85

90

Explanation

This question tests middle school quantitative reasoning skills, specifically using a function rule to determine output. Function rules allow us to calculate output values by substituting input values into an algebraic expression. In this question, the car distance rule d = 40t + 5 is used to find distance d when time t = 2. Choice A is correct because substituting 2 for t yields d = 40(2) + 5 = 80 + 5 = 85, demonstrating proper function application and order of operations. Choice C (80) represents the common error of forgetting to add the constant term, calculating only 40(2). Choice D (90) might result from calculating 40(2) + 10, while Choice B (45) could come from adding before multiplying. To help students, stress the importance of following order of operations systematically. Using distance-time relationships helps students connect algebra to physics concepts.

7

Store cost rule: $y = 6x + 1$. Find $y$ when $x = 3$.

7

10

18

19

Explanation

This question tests middle school quantitative reasoning skills, specifically using a function rule to determine output. Function rules allow us to calculate output values by substituting input values into an algebraic expression. In this question, the store cost rule y = 6x + 1 is used to find total cost y when x = 3. Choice A is correct because substituting 3 for x yields y = 6(3) + 1 = 18 + 1 = 19, demonstrating proper function application and order of operations. Choice B (18) represents the common error of forgetting to add the constant term, calculating only 6(3). Choice C (10) might result from calculating 3(3) + 1, while Choice D (7) could come from adding 6 + 1. To help students, stress the importance of following each step: multiply first, then add. Store pricing contexts help students connect abstract algebra to everyday situations.

8

Store total cost: $y = 4x + 2$. Find $y$ when $x = 5$.

14

18

22

28

Explanation

This question tests middle school quantitative reasoning skills, specifically using a function rule to determine output. Function rules allow us to calculate output values by substituting input values into an algebraic expression. In this question, the function y = 4x + 2 represents total cost at a store, where we need to find y when x = 5. Choice A is correct because substituting 5 for x yields y = 4(5) + 2 = 20 + 2 = 22, demonstrating proper function application and order of operations. Choice B (28) might result from incorrectly calculating 4(5) as 26, while Choice C (14) could come from only calculating 4(5) - 6. To help students, emphasize following order of operations: multiply first, then add. Using real-world contexts like store pricing helps students connect abstract algebra to practical situations.

9

A car travels at constant speed: $d = 50t$. Find $d$ when $t = 3$.

47

53

100

150

Explanation

This question tests middle school quantitative reasoning skills, specifically using a function rule to determine output. Function rules allow us to calculate output values by substituting input values into an algebraic expression. In this question, the function d = 50t represents distance traveled at constant speed, where we need to find d when t = 3. Choice A is correct because substituting 3 for t yields d = 50(3) = 150, demonstrating proper function application. The other choices represent common errors: Choice C (47) and B (53) might result from subtraction or addition errors, while Choice D (100) could come from multiplying by 2 instead of 3. To help students, emphasize the importance of careful substitution and multiplication. Practice with real-world contexts like distance-speed relationships helps students understand the practical application of function rules.

10

What is the "zip" of the number 38?

10

13

42

44

Explanation

The correct answer is 13. First, divide 38 by 5. \(38 \div 5 = 7\) with a remainder of 3. So, the whole number quotient is 7 and the remainder is 3. The rule is to add the quotient (7) and twice the remainder (\(2 \times 3 = 6\)). The result is \(7 + 6 = 13\).

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