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 = = Solution is correct! m

Example 1 m + 18 = 34 Look for variable -18 Do the inverse m = 16 Write what m is m + 18 = = 34 substitute in m 34 = Solution is correct!

Always remember to check your solution to the equation.

Example 2 68 = y + 43 Look for variable -43 Do the opposite 25 = y Write what y is 68 = y = Plug in y 68 = Solution is correct!

Example 3 t - 14 = 22 Look for variable Do the inverse t = 36 Write what t is t - 14 = = 22 Substitute in t 22 = Solution is correct!

Try These r + 5 = m - 26 = = x a + 39 = 56 r = 13 m = = 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?