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Function machines: 4th grade math

Input–output rules ("function machine"). A free 4th grade lesson plan, a question set with answers and a printable sheet with its key. Copy it and make it yours.

Lesson plan

Goal

  • Students can do this: input–output rules ("function machine").

Teach (10 min)

  • A function is a rule. You put in an input and the rule gives you an output.
  • Rule: multiply by 3, then add 2. Input 4: 4 × 3 = 12, then 12 + 2 = 14. The output is 14.
  • Work one example on the board while students say each step aloud, then do one together.

Practise (15 min)

  • Students work the printable sheet in pairs, then alone.
  • Or practise it as a game with no sign-up: https://peabody.kids/math/funcs.rule?lesson=8-funcs-rule-1&at=4

Exit ticket (5 min)

  • Three questions on a slip:
  • 1. A rule takes an input and gives an output. The rule: subtract 3. What is the output when the input is 6?
  • 2. A rule takes an input and gives an output. The rule: add 6. What is the output when the input is 2?
  • 3. A rule takes an input and gives an output. The rule: subtract 3. What is the output when the input is 6?

Question set

10 questions that read in words, easiest first. Questions that need a picture are on the printable sheet below.

  1. A rule takes an input and gives an output. The rule: subtract 3. What is the output when the input is 6?
  2. A rule takes an input and gives an output. The rule: add 6. What is the output when the input is 2?
  3. A rule takes an input and gives an output. The rule: subtract 3. What is the output when the input is 6?
  4. A rule takes an input and gives an output. The rule: add 4. What is the output when the input is 6?
  5. A rule takes an input and gives an output. The rule: multiply by 7. What is the output when the input is 2?
  6. A rule takes an input and gives an output. The rule: multiply by 2. What is the output when the input is 7?
  7. A rule takes an input and gives an output. The rule: multiply by 4. What is the output when the input is 5?
  8. A rule takes an input and gives an output. The rule: add 6. What is the output when the input is 2?
  9. A rule takes an input and gives an output. The rule: add 9, then multiply by 5. What is the output when the input is 2?
  10. A rule takes an input and gives an output. The rule: add 3, then multiply by 4. What is the output when the input is 9?
Answers
  1. output = 3
  2. output = 8
  3. output = 3
  4. output = 10
  5. output = 14
  6. output = 14
  7. output = 20
  8. output = 8
  9. output = 55
  10. output = 48

Printable sheet

Name: ____________________   Date: ____________

Function machines (4th grade)

  1. A rule takes an input and gives an output. The rule: multiply by 4. What is the output when the input is 2?
  2. A rule takes an input and gives an output. The rule: add 7. What is the output when the input is 9?
  3. A rule takes an input and gives an output. The rule: subtract 1. What is the output when the input is 8?
  4. A rule takes an input and gives an output. The rule: subtract 3. What is the output when the input is 7?
  5. A rule takes an input and gives an output. The rule: add 2. What is the output when the input is 1?
  6. A rule takes an input and gives an output. The rule: multiply by 9, then add 3. What is the output when the input is 7?
  7. A rule takes an input and gives an output. The rule: divide by 4, then multiply by 8. What is the output when the input is 16?
  8. A rule takes an input and gives an output. The rule: multiply by 5, then add 8. What is the output when the input is 7?
  9. A rule takes an input and gives an output. The rule: subtract 3, then add 7. What is the output when the input is 7?
  10. A rule takes an input and gives an output. The rule: add 2, then multiply by 2. What is the output when the input is 10?
  11. A rule takes an input and gives an output. The rule: subtract 7, then add 12. What is the output when the input is 3?
  12. A rule takes an input and gives an output. The rule: add 9, then multiply by 5. What is the output when the input is 6?
Key
  1. output = 8
  2. output = 16
  3. output = 7
  4. output = 4
  5. output = 3
  6. output = 66
  7. output = 32
  8. output = 43
  9. output = 11
  10. output = 24
  11. output = 8
  12. output = 75

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