Download Summary of Addition and Subtraction Basic Fact Strategies

Summary of Addition and Subtraction Strategies
Basic Facts are the facts that are memorized and then used to figure out
the facts that are not memorized. They are basic because they are the basis
for all of the other facts.
The strategies that we use to help the students make connections to math
concepts and skills are step-by-step procedures that the students learn to do
without paper and pencil. These strategies are most effective when the basic
facts are memorized.
Addition Strategies
Counting up is a simple way to add a small quantity to a larger quantity.
Example: for 14 + 3, a child might count up three saying 15, 16, 17.
N + 0: Plus zero always equals the number
N + 1: Plus one is always one more than the number
N + 2: Count up two from the number
N + 3: Count up three from the number
[N means number.]
Although counting up can be used to add larger numbers together, it is time
consuming and not as efficient as other strategies.(*) We encourage counting
up for adding small quantities like 1, 2, or 3 to an amount.
Double facts are relatively easy to learn and become powerful anchors for
other addition facts. Students quickly learn and identify patterns in the below
sequence.
1+1=2 2+2=4 3+3=6 4+4=8 5 + 5 = 10
6 + 6 = 12 7 + 7 = 14 8 + 8 = 16 9 + 9 = 18
10 + 10 = 20
Double neighbors are also called “doubles-plus-one” and “doubles-plustwo.” The strategy is to double the smaller addend and add one or two more.
Ifyouknow6+6is12 → then6+7isjust6+6+1=13. Ifyouknow5+5is10 →
then5+7isjust5+5+2=12.
Make-Ten:
Ten’s partners are combinations of numbers that equal 10. Understanding
how numbers relate to 10 (ex: 8 is two away from 10) is critical for fluent
computation.
0 + 10 = 10 1 + 9 = 10 2 + 8 = 10
3 + 7 = 10 4 + 6 = 10 5 + 5 = 10
Make ten is an important strategy because it is easy to add a number to 10
(or to a multiple of 10). This is an important feature of our base-10 number
system.
For 6+9, think 5+10→split the 6 to make the problem 5+1+9
For 6+8, think 4+10→split the 6 to make the problem 4+2+8
(*) To add 14 + 9, students can count up nine (they’d probably count out
nine fingers while saying 15, 16, 17, 18, 19, 20, 21, 22, 23); this is a reliable
yet cumbersome method. Over time, students develop quicker ways to
compute.
For example, to solve 14 + 9 a child might:
a) Round the nine to a ten: so that 14+9 becomes 14+10 – 1 which is 24–1 =
23.
b) Split the nine apart in to six plus three: so that 14+9 becomes 14+6+3 =
20 + 3 = 23.
.Subtraction
Strategies
N – 0: Minus zero always equals the number �
N – 1: Minus one is always one less than the number �
N – 2: Count back two from the number �
N – 3: Count back three from the number
Use What You Already Know
�Ten’s Partners:
�Double Facts:
�Double Neighbors:
�Make
Ten’ s:
Think Addition!
If you know that 9+1, 8+2, 7+3, 6+4, and 5+5 all equal 10, then apply this
knowledge to subtraction facts:
10 – 9 = 1 10 – 7 = 3 10 – 4 = 6 10 – 5 = 5 and so forth.
If you know the sums of 9+9, 8+8, 7+7, and 6+6, then you know the
differences for:
18 – 9 = 9 16 – 8 = 8 14 – 7 = 7 12 – 6 = 6
By knowing double facts, you also can solve “close” facts:
16 – 8 = 8, so 17 – 8 = 9 14 – 7 = 7, so 13 – 7 = 6
Convert a minus 9 to minus 10, and then add 1 back:
For 25 – 9 = ?, try 25 – 10 + 1 = 16
Convert a minus 8 to a minus 10, and then add 2 back:
For 33 – 8 = ?, try 33 – 10 + 2 = 25
�
Turn Subtraction Problems Into Addition Problems:
17–12=? →turn into 12+□=17
16– 9=? → turn into 9+□ =16
Split Numbers
�Break Numbers Down Into Parts For Easier Computation:
For 34 – 7 = ?, you could do 34 – 4 – 3 = ? [which is 30-3 = 27] For 55 – 8 =
?, try 55 – 5 – 3 = ? [which is 50 – 3 = 47]