Solving Addition and Subtraction Equations
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Nov 16, 2014
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Solving Addition and Subtraction Equations
An equation is a
mathematical sentence
that contains an equal sign.
The expression on the left and right side of the equal
sign are equivalent. One or
both sides may contain a variable.
A variable is a letter or
symbol that stands for a
number.
To solve an equation, you
must find what the variable
represents so that the two
parts are equal.
Equations are like balance scales. In order to keep a scale balanced you must have the same amount of weight on both sides.
If I took one block away from the left side, what would I have to do to keep
the scale from tipping?
If I added 6 more apples to the right side, how could I keep the scale from
tipping?
To keep an equation equal, we must do exactly the same
thing to each side of the equation. If we
add a number to one side, we must add
that same number to the other side and
vice versa.
Addition and subtraction are called “inverse operations”.
Multiplication and
division are inverse
operations, too!
for Solving Addition and Subtraction Equations
1. Look to see what side the variable
is on.
2. Decide what
operation is being shown.
3. Do the inverse of
that operation to both sides.
4. Write what
number the variable
stands for (ex: a = 2).
5. Check the solution by “substituting” the number back into the equation to see if the sides are equivalent.
Example 1 (bar model) m + 18 = 34 Look for variable
Do the inverse What number does m represent?
m = 16
Substitute in m
16 + 18 = 34
34 = 34
Solution is correct!
m 18
34
16 18
34
Example 1m + 18 = 34 Look for variable
-18 -18 Do the inverse
m = 16 Write what m is
m + 18 = 34
16 + 18 = 34 substitute in m
34 = 34 Solution is correct!
Always remember to check your solution to the
equation.
Example 2 68 = y + 43 Look for variable
-43 -43 Do the opposite
25 = y Write what y is
68 = y + 43
68 = 25 + 43 Plug in y
68 = 68 Solution is correct!
Example 3 t - 14 = 22 Look for variable
+ 14 +14 Do the inverse
t = 36 Write what t is
t - 14 = 22
36 - 14 = 22 Substitute in t
22 = 22 Solution is correct!
Try These...1. r + 5 = 18
2. m - 26 = 59
3. 102 = x - 15
4. a + 39 = 56
r = 13
m = 85
117 = x
a = 17
Prediction:You will show all
of the steps (including
checking) as you have been shown
today
Are there any questions
about solving addition or subtraction equations?
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