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Addition Shortcuts

Round to the nearest friendly number, then adjust.

When to use

Adding two numbers where one is close to a round number.

Steps

  1. 1.Round the smaller number to the nearest 10 or 100
  2. 2.Add the rounded number
  3. 3.Adjust for the rounding

Example: 99 + 929

Round 99 up to 100 (added 1 too many)

100 + 929 = 1,029

Subtract the extra 1: 1,029 - 1 = 1,028

Mental approach

99 + 929: think 100 + 929 = 1,029 then subtract 1 = 1,028.

Pen & paper approach

Standard column addition, but check with rounding for speed.

Tips

  • •Always round the number that's closest to a round number
  • •75 + 701: no rounding needed, just 776
  • •For 3+ digit addition: add left to right (hundreds, tens, ones)

Try it yourself

88 + 945

199 + 367

47 + 685