Mental Math Strategies Break Apart and Make a Ten by HC120617121326

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									                          Mental Math – Break Apart Strategy

Three steps to using the break apart strategy to find a sum:

78 + 95 = _____

1) Add the tens: 70 + 90 = 160

2) Add the ones: 8 + 5 = 13

3) Add the sums: 160 + 13 = 173. So 78 + 95 = 173.

Three steps to using the break apart strategy to find a difference:

46 – 21 = _____

1) Subtract the tens: 40 – 20 = 20

2) Subtract the ones: 6 – 1 = 5

3) Add the differences: 20 + 5 = 25. So 46 – 21 = 25.



                          Mental Math – Make a Ten Strategy

67 + 24 = _____                                                When using Make a Ten
Three steps using the make a ten strategy to find a sum:       Strategy to find the sum,
67 + 24 = _____
                                                               you must add to make
                                                               one of the numbers a
1) Change one number to a multiple of 10: 67 + 3 = 70
                                                               ten. Then you subtract
2) Adjust the other number: 24 – 3 = 21                        the number you added
3) Add: 70 + 21 = 91. So 67 + 24 = 91.                         from the other number.

Three steps using the make a ten strategy to find a difference:

86 – 29 = _____
                                                               When using Make a Ten
1) Change the second number to a multiple of 10: 29 + 1 = 30   Strategy to find a
2) Adjust the other number: 86 + 1 = 87                        difference, you must add
3) Subtract: 87 - 30 = 57. So 86 – 29 = 57.
                                                               to make one of the
                                                               numbers a ten. Then
                                                               you add the same
                                                               amount to the other
                                                               number in the problem.

								
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