Parent Support for Addition and
Subtraction Strategies Used at School
Below are examples of the types of addition and subtraction
strategies that have been shared in class. In looking them over,
it is important to keep a few things in mind:
Estimating the result is very powerful because it helps
students think about the quantities they are using and what
to expect as a result.
Students may use a combination of strategies in solving a
problem and that is okay. What works for one person, may
not work for another.
If a strategy does not make sense for your child, please do
not force it on them as a memorized procedure. Rather,
encourage students to build off of what they already know
to develop strategies over time.
The standard algorithm is not used as an example below.
Some students have learned this strategy at home. They
are allowed to use it as a possible strategy in class if they
can explain why they do what they do. For example, in the
problem 321-160 students should be able to explain that
they are borrowing a hundred from the 300 to make it 121-
60=61. Then they have 200 left and need to subtract 100
from that to come up with 100. Thus the answer is 161. If
students explain it as borrowing 1 from the 3 to make the 2
a 12 and 12-6=6, they are not demonstrating an
understanding of the problem and this strategy should not
be used yet. Remember, the traditional algorithm is just a
shorthand way of solving a subtraction problem. In order to
use that strategy successfully, children must understand
the processes behind the shortcut.
Most importantly, students should be using what they know
about numbers to simplify the problem. This will lead to
procedures that make more sense.
Created by Shannon Ducharme
Somerset Elementary
Addition Strategies
Left-to-Right Addition—When students work with the largest quantities
first it’s easier to maintain a good sense of what the final sum should be. It
also helps them to see the whole quantities rather than individual digits (for
example, the 4 in 47 is 40, not 4).
47 + 48 =
40 + 40 = 80
7 + 8 = 15
80 + 15 = 95
Rounding to Nearby Landmarks—Changing a number to a more familiar one
that is easier to compute. Multiples of 10 and multiples of 100 are especially
useful landmarks for children at this age.
199 + 149 =
Think of it as 200 + 150 = 350.
Then subtract 2 to compensate for the 2 added on at the
beginning. 350 – 2 = 348
Changing the Order of the Numbers—Simply changing the order of the
numbers you are adding is often a great help.
23 + 46 + 7 =
23 + 7 = 30
30 + 46 = 76
Created by Shannon Ducharme
Somerset Elementary
Subtraction Strategies
Break and Subtract—Sometimes students try to break apart both numbers,
as they would in the Left-to-Right addition strategy. However, this can
cause problems when the first number is smaller than the second. Unless
students have effective strategies for dealing with this issue, they should
get into the habit of separating only the number being subtracted.
74 – 49 = Or
49 is 40 and 9 • 49 is 40 and 5 and 4
74 – 40 = 34 • 74 – 40 =34
34 – 9 = 25 • 34 – 4 = 30
• 30 – 5 = 25
Adding Up—In this strategy students use addition to help solve a
subtraction problem.
372 – 218 =
218 + 2 = 220
220 + 80 = 300 2 + 80 + 72 = 154
300 + 72 = 372
Adjusting Numbers—This can be done in numerous ways. The goal is to
create numbers that are easier to work with.
447 – 297 =
450 – 300 = 150
By adding three to each of the numbers the answer will remain
the same because the numbers are still the same distance apart.
321 – 165 =
Adjust 321 to 320 (321 - 1 = 320)
320 – 165 = 155
Add one to the answer because you actually subtract from a
number that is one greater than 320.
155 + 1 = 156
Created by Shannon Ducharme
Somerset Elementary