Mental maths strategies

Partitioning and near doubles to add quickly in your head

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Try each question. If you're stuck, leave it and come back. The answer key is on the last page.

1
Use partitioning: 35 + 27 = 30 + 20 + 5 + 7 = ___ 30 + 20 + 5 + 7 = ___
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2
Near doubles: 24 + 25 = double 24 + 1 = ___ double 24 + 1 = ___
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3
Which is the best partitioning for 46 + 32? A) 40 + 30 + 6 + 2 B) 4 + 3 + 6 + 2 C) 46 + 30 + 2 D) 40 + 32 + 6
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4
Use partitioning: 22 + 13 = 20 + 10 + 2 + 3 = ___ 20 + 10 + 2 + 3 = ___
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5
Partition to add: 53 + 26 = ___ 53 + 26 = ___
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6
Use near doubles to work out 17 + 18. A) 34 B) 35 C) 36 D) 37
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7
True or false? Using near doubles, 30 + 31 = 61. A) True B) False
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8
What is 48 + 36 using partitioning? A) 74 B) 82 C) 84 D) 94
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9
Use partitioning: 67 + 25 = ___ 67 + 25 = ___
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10
Which strategy gives the correct answer for 38 + 40? A) Double 38 + 1 B) Double 40 - 2 C) Double 38 + 4 D) Double 40 - 4
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Answer key

Mental maths strategies · for parents and teachers

1
62
30 + 20 = 50, and 5 + 7 = 12. 50 + 12 = 62.
2
49
Double 24 = 48, and 48 + 1 = 49. Near doubles use a known double plus or minus a small amount.
3
40 + 30 + 6 + 2
46 = 40 + 6 and 32 = 30 + 2, so we partition into 40 + 30 + 6 + 2.
4
35
20 + 10 = 30, and 2 + 3 = 5. 30 + 5 = 35.
5
79
50 + 20 = 70, and 3 + 6 = 9. 70 + 9 = 79.
6
35
Double 17 = 34, and 34 + 1 = 35. (Or double 18 = 36, and 36 - 1 = 35.)
7
True
True. Double 30 = 60, and 60 + 1 = 61. So 30 + 31 = 61.
8
84
40 + 30 = 70, and 8 + 6 = 14. 70 + 14 = 84.
9
92
60 + 20 = 80, and 7 + 5 = 12. 80 + 12 = 92.
10
Double 40 - 2
Double 40 = 80, and 80 - 2 = 78. Since 38 = 40 - 2, this gives the correct answer (38 + 40 = 78).