Solving Equations · One-step equations · 2.2

Subtract to solve.

When a number is added to x, subtract it from both sides. x + 7 = 10 → subtract 7 → x = 3.

01 / THE IDEA

See it work.

Watch the method

Subtract to solve

x + 7 = 10 → subtract 7 from both sides → x = 3.

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x+7=10x + 7 = 10
1

The equation

Solve for x — find the value that makes both sides equal.

x+7=10x + 7 = 10
2

Move the constant

Subtract 7 from both sides.

x=3x = 3
3

Read the solution

x is already by itself.

x=3x = 3
02 / YOUR TURN

Practice until it feels automatic.

Your turn

Solve for x.

Type the value of x — a number or a fraction like 3/2.

streak 0
best 0
…x =
— / WHY IT WORKS

The idea underneath.

Subtract to undo a plus

If x + a = b, then x = b − a (subtract a from both sides).

Why it works

x + 7 = 10 means x is 7 less than 10.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Solve x + 2 = 14

1

The equation

Solve for x — find the value that makes both sides equal. x + 2 = 14

2

Move the constant

Subtract 2 from both sides. x = 12

3

Read the solution

x is already by itself. x = 12

EX 2medium

Solve x + 3 = 7

1

The equation

Solve for x — find the value that makes both sides equal. x + 3 = 7

2

Move the constant

Subtract 3 from both sides. x = 4

3

Read the solution

x is already by itself. x = 4

EX 3hard

Solve x + 2 = 7

1

The equation

Solve for x — find the value that makes both sides equal. x + 2 = 7

2

Move the constant

Subtract 2 from both sides. x = 5

3

Read the solution

x is already by itself. x = 5

04 / COMMON TRAPS

Where students slip.

Trap

Adding instead of subtracting.

Fix

To undo + 7, subtract 7.

Trap

Changing one side only.

Fix

Subtract from both sides.

05 / QUIZ

Test yourself.

The Test

12 problems across three tiers. Auto-graded on submit. Hints and a full walkthrough on every question. Your work is saved on this device — sign in to keep it across devices.

0/12Answered
How to answerType just the value. Formatting won't trip you up — we ignore spaces, capital letters, commas, and subscript style, so t₁ = 5, d = 3 and t1=5,d=3 both count. For a list of numbers, separate them with commas (e.g. 3, 10, 17).
Core

Core (4)

C1

Solve x + 1 = 8

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
C2

Solve x + 1 = 9

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
C3

Solve x + 3 = 7

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
C4

Solve x + 7 = 9

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
Apply

Apply (4)

A1

Solve x + 5 = 17

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
A2

Solve x + 9 = 19

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
A3

Solve x + 1 = 13

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
A4

Solve x + 5 = 13

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
Extension

Extension (4)

E1

Solve x + 9 = 19

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
E2

Solve x + 8 = 12

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
E3

Solve x + 8 = 19

Need a hint?
  • Subtract the added number.
  • Do it to both sides.
E4

Solve x + 9 = 19

Need a hint?
  • Subtract the added number.
  • Do it to both sides.