One- and two-step equations

To get $x$ alone, you undo what was done to it. The last thing done gets undone first. In $3 x + 5$ , you first multiply by 3 and then add 5, so you subtract 5 first and then divide by 3.

Work through it

$3 x + 5 = 20$

Subtract 5: $3 x = 15$

Divide by 3: $x = 5$

$7 - 2 x = 15$

Subtract 7: $- 2 x = 8$

Divide by $- 2$ : $x = - 4$

$\frac{x - 4}{3} = 5$

Multiply by 3: $x - 4 = 15$

Add 4: $x = 19$

Watch out for this

$7 - 2 x = 15$ becomes $5 x = 15$ .

7 and $- 2 x$ aren't like terms. You can't combine them, so move the 7 first.

Your turn

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