operations · Year 3 · AC9M3A02

Mental strategies: split and compensate

Split strategy: break numbers into tens and ones. For 47 + 36, add the tens (70), add the ones (13), then combine: 83. For subtraction, take away the tens and then the ones. Compensation: when a number is close to a round number, use the round number and then fix it. For 46 + 29, add 30 to get 76, then take away the extra 1: 75.

Sample questions

Split into tens and ones: 75 + 19 = 70 + 10 + 5 + 9 = ?

  1. Tens: 70 + 10 = 80. Ones: 5 + 9 = 14.
  2. 14 is 1 ten and 4 ones, so 80 + 14 = 94.
  3. So 75 + 19 = 94.

Answer: 94

Split into tens and ones: 36 + 34 = 30 + 30 + 6 + 4 = ?

  1. Tens: 30 + 30 = 60. Ones: 6 + 4 = 10.
  2. 10 is 1 ten and 0 ones, so 60 + 10 = 70.
  3. So 36 + 34 = 70.

Answer: 70

Split into tens and ones: 64 + 16 = 60 + 10 + 4 + 6 = ?

  1. Tens: 60 + 10 = 70. Ones: 4 + 6 = 10.
  2. 10 is 1 ten and 0 ones, so 70 + 10 = 80.
  3. So 64 + 16 = 80.

Answer: 80

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