SOLVE IT
Solve: 2x + 7 = 15
x = 4
A student solves 2x + 4 = 12 and gets x = 8. What did they do wrong?
They added 4 instead of subtracting 4 first. The correct answer is x = 4.
Solve: 2x - 3 = 11
x=7
In 3x + 5 = 20, what should you undo first?
minus 5 from both sides
Solve: x/2 + 3 = 9
x = 12
Solve: 3x - 5 = 16
x = 7
Is this correct? 3x - 6 = 15 → 3x = 9 → x = 3
Yes
Solve: 6x + 2 = 38
x=6
What operation undoes +8
Solve: x/4 - 2 = 6
x=32
Solve: 4x + 9 = 29
x = 5
Find the mistake: 5x + 10 = 35 → 5x = 45 → x = 9
The student added 10 instead of subtracting 10. Correct: 5x = 25, so x = 5.
Solve: 8x - 13 = 51
x=8
What operation undoes multiplication by 6?
Division by 6
Solve: 5x + 1 = 26
x=5
Solve: 7x - 8 = 34
x = 6
Find the mistake: 4x - 7 = 21 → 4x = 14 → x = 3.5
The student should add 7: 4x = 28, so x = 7.
Solve: 12x + 5 = 89
x=7
For 7x - 4 = 24, what is the first step?
+ 4
Solve: 10x - 15 = 45
x = 6
Solve: 9x + 12 = 75
x = 7
Why must you undo addition/subtraction before multiplication/division when solving a 2-step equation?
It reverses the order of operations and isolates the variable step by step.
Solve: 15x - 20 = 100
x=8
Create a 2-step equation whose solution is x = 10.
Create a 2-step equation whose solution is x = 10.
Example: 3x + 5 = 35. Any valid 2-step equation with x = 10 works.
Challenge: Solve 4(x + 3) = 28.
x = 4