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Compatible Numbers

Compatible Numbers. Susan Phillips Lee’s Summit, MO. Using Mental Math. Key Term compatible numbers. Learn how to . . . use compatible numbers for mental math decide when to use mental math, paper and pencil, or a calculator. Let’s Begin!. Discussion:.

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Compatible Numbers

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  1. Compatible Numbers Susan PhillipsLee’s Summit, MO

  2. Using Mental Math Key Term • compatible numbers

  3. Learn how to . . . • use compatible numbers for mental math • decide when to use mental math, paper and pencil, or a calculator

  4. Let’s Begin!

  5. Discussion: • Do you always need to use pencil and paper or a calculator to work addition and multiplication problems?

  6. When you need an exact answer, sometimes mental math is the best choice.

  7. Two students are running for student council. Here are some of the voting results. Candidate A Room 1 14 VotesRoom 2 17 VotesRoom 3 16 VotesRoom 4 13 Votes Which candidate’s votes are easier to add quickly in your head? Candidate BRoom 1 19 VotesRoom 2 12 VotesRoom 3 17 VotesRoom 4 14 Votes Why?

  8. Candidate A Room 1 14 VotesRoom 2 17 VotesRoom 3 16 VotesRoom 4 13 Votes 14 and 16 are compatible numbers. Compatible numbers have sums or products that are easy to compute. 13 and 17 are compatible numbers.

  9. 19 + 27 + 11 30 19 + 11 are compatible numbers that equal 30. 30+ 27 = 57

  10. 26 + 55 + 35 + 54 55 + 35are compatible numbers that equal 90. 26 + 54are compatible numbers that equal 80. 90 + 80= 170

  11. Use mental math to solve each problem. Discuss the compatible numbers you use with your group.

  12. 40 + 60 + 87

  13. 42 + 24 + 8 + 26

  14. 113 + 76 + 74 + 87

  15. 17 + 8 + 30 + 75

  16. Checking for compatible numbers can also help you multiply quickly in your head. Look for numbers with products that are easy to compute.

  17. 7 4 5 7 20 = 140 4 and 5 are compatible numbers.

  18. 4 17 25 17 100 = 1700 4 and 25 are compatible numbers.

  19. Use mental math to find each product. • Discuss the compatible numbers you use with your group. 2 8 15 9 5 4 25 6 4 4 5 9 5 4

  20. The Great Arithmetic Race • Choose your roles. One person will use mental math, one will use paper and pencil, one will use a calculator and one will be the record keeper. • When you click the mouse, a problem will appear for the race. Each person will calculate the answer using only his assigned method. (If you are paper and pencil – you must write down the problem and work it out on paper…) • The first person to get the correct answer gets a point.

  21. 5 5 3

  22. 13 + 17 + 12

  23. 100 x 13

  24. 25 + 42 + 25

  25. 2 15 4

  26. 6 + 19 + 14 + 211

  27. 2 3 3 25

  28. 20 8 5 3

  29. 12 + 17 + 8 + 3

  30. 32 + 45 + 5 + 8

  31. Discussion: • Was the calculator always the quickest, best tool? • When is it best to use pencil and paper? • When is it best to use mental math? • When is it best to use a calculator?

  32. Congratulations! You have just completed Compatible Numbers

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