Grade: Grade 1 Subject: SAT/ACT Skills Unit: Mental Math Warmups Lesson: 5 of 6 SAT Domain: ProblemSolving+DataAnalysis ACT Section: Math

Review Mistakes

Learn

Making mistakes is part of learning! The most important thing is to understand why you made a mistake so you can do better next time.

Common Mental Math Mistakes

Mistake 1: Counting Wrong

Example: For 6 + 3, a student counts "6... 7, 8" and says 8.

What happened: They only counted 2 more instead of 3 more.

Fix it: Use your fingers to keep track: 7 (one finger), 8 (two fingers), 9 (three fingers). The answer is 9!

Mistake 2: Mixing Up + and -

Example: For 8 - 3, a student says 11.

What happened: They added instead of subtracting!

Fix it: Look carefully at the sign. The minus sign (-) means take away. 8 - 3 = 5.

Mistake 3: Rushing Too Fast

Example: For 7 + 2, a student quickly says 8.

What happened: They went too fast and made a small error.

Fix it: Take a breath. Double-check before saying your answer. 7 + 2 = 9.

How to Learn from Mistakes

  1. Find the mistake: Look at the problem and your wrong answer.
  2. Ask why: What went wrong? Did you count wrong? Mix up signs?
  3. Do it again: Solve the problem correctly this time.
  4. Practice more: Do similar problems to get better.

Examples

Let us practice finding and fixing mistakes.

Example 1: Find the Mistake

A student said 5 + 4 = 8. Is this correct?

Solution: No! Let us count: 5... 6, 7, 8, 9. The correct answer is 9. The student counted only 3 instead of 4.

Example 2: Find the Mistake

A student said 10 - 4 = 14. Is this correct?

Solution: No! The student added instead of subtracting. 10 - 4 = 6.

Example 3: Find the Mistake

A student said 3 + 3 = 9. Is this correct?

Solution: No! Maybe the student was thinking of 3 + 6 = 9. But 3 + 3 = 6.

Practice

Each problem shows a mistake. Find the correct answer!

  1. A student said 4 + 5 = 8. What is the correct answer?

    Show Answer

    The correct answer is 9. The student was off by 1.

  2. A student said 9 - 2 = 11. What is the correct answer?

    Show Answer

    The correct answer is 7. The student added instead of subtracted.

  3. A student said 6 + 1 = 8. What is the correct answer?

    Show Answer

    The correct answer is 7. The student counted too many.

  4. A student said 11 - 3 = 7. What is the correct answer?

    Show Answer

    The correct answer is 8. The student took away too much.

  5. A student said 2 + 7 = 8. What is the correct answer?

    Show Answer

    The correct answer is 9. The student was off by 1.

  6. A student said 8 - 4 = 3. What is the correct answer?

    Show Answer

    The correct answer is 4. The student took away too much.

  7. A student said 5 + 6 = 10. What is the correct answer?

    Show Answer

    The correct answer is 11. The student did not count far enough.

  8. A student said 12 - 5 = 6. What is the correct answer?

    Show Answer

    The correct answer is 7. The student took away too much.

  9. A student said 7 + 3 = 9. What is the correct answer?

    Show Answer

    The correct answer is 10. The student was off by 1.

  10. A student said 10 - 6 = 5. What is the correct answer?

    Show Answer

    The correct answer is 4. The student did not take away enough.

Check Your Understanding

Think about these questions:

  1. What are three common mistakes people make with mental math?
  2. What should you do after you find a mistake?
  3. Why is it good to make mistakes when learning?
Show Answers
  1. Counting wrong, mixing up + and -, and rushing too fast.
  2. Figure out why you made the mistake, solve it correctly, and practice more.
  3. Mistakes help you learn what you need to work on. Everyone makes mistakes!

Next Steps

  • Keep a list of problems you miss and practice them
  • Do not get upset about mistakes - use them to learn!
  • Move on to Mixed Set for a final challenge