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All courses Math Foundations · MF.EQ.5 32 of 60
Solve one-step equations and interpret the solution in context.

Undo addition or subtraction in one step

Problem
Solve the equation: \(x~+~7~=~12\). What is \(x\)?
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Hint

Look at the operation on x. Since 7 is added to x, start by subtracting 7 from both sides.

Use inverse operations: subtraction undoes addition and keeps the equation balanced when you do it to both sides.

Solution walkthrough

01

Identify the inverse operation

\[x~+~7~=~12\]

Seven is added to x, so subtracting 7 will isolate x.

02

Subtract seven from both sides

\[x~+~7~-~7~=~12~-~7\]

Applying the same subtraction to both sides preserves equality and cancels +7.

03

Solve and check

\[x~=~5;~5~+~7~=~12\]

The solution 5 makes the original equation true.

04

State the solution

\[x~=~5\]

Five is the unique number that is 7 less than 12.

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Another way

  1. Ask which number plus 7 equals 12; the missing addend is 5.

!

Common mistake

Do not add 7 to 12. To undo the +7 attached to x, subtract 7 from both sides.

Solution walkthrough video