Mental Computation Strategies: Addition Go to Articles
It is essential that all students are able to calculate mentally as well as with paper and pencil. Students can make mental calculations quickly and easily with the help of strategies. There are mental computation strategies for each of the four operations: addition, subtraction, multiplication, and division. Strategies for addition are explained here.
Adding the places
Start with one addend, then add the value of the digits of the other addend(s).
See 35 + 23
Think 35 + 20 + 3
Bridging to ten
Start with one addend, count up to the next multiple of 10 (100, 1000 etc.), then add the balance of the second addend.
See 17 + 8
Think 17 + 3 + 5
Synonyms: bridge the decades; bridge to ten; make a ten; make to ten; use ten
Compensating
Round one or both addends before adding. Then adjust the answer to compensate for the rounding.
See 28 + 36
Think (30 + 36) – 2
Synonyms: compensation; round and adjust; round or adjust; use a nearby number
Counting on
Start with one addend, then count on parts (not places) of the other addend.
See 58 + 24
Think 58 + 10 + 10 + 4
Synonym: jump
Sub-strategies: count on 1; count on 2; count on 3; count on 0
Using compatible addends
Choose pairs of addends to make the calculation more manageable. This strategy applies only when there are three or more addends.
See 14 + 23 + 16
Think 14 + 16 + 23
Synonym: use compatible pairs
Using doubles
Use a known nearby double.
See 7 + 8 = ___
Think 7 + 8 = 15 because 7 + 7 = 14
Synonym: near doubles
Sub-strategies: double plus 1; double plus 2
Using place value
Expand the addends into places before adding the value of the digits in each place.
See 56 + 17
Think 50 + 10 + 6 + 7 or 6 + 7 + 50 + 10
Synonym: split
(For doubling)
Split one of the addends into places, double the value of the digits in each place, then add the doubled values.
See 12 + 12
Think double 10 + double 2
From The ORIGO Handbook of Mathematics Education, 2007, ORIGO Education
These addition strategies, as well as strategies for subtraction, multiplication, and division, are explained in The ORIGO Handbook of Mathematics Education.
Bibliography
Burnett, J. (2001). Mastering mental maths: Addition. Brisbane, Australia: Prime Education.
Burnett, J., & Irons, C. (2005). GO maths teacher sourcebook: Level 2B. Brisbane, Australia: ORIGO Education.
Irons, C., Burnett, J., & Turton, A. (2007). The book of facts: Addition. Brisbane, Australia: ORIGO Education.
The ORIGO handbook of mathematics education. (2007). Brisbane, Australia: ORIGO Education.
