Solving Equations · One-step equations · 2.1

Add to solve.

When a number is subtracted from x, add it to both sides to undo. x − 5 = 3 → add 5 → x = 8.

01 / THE IDEA

See it work.

Watch the method

Add to solve

x − 5 = 3 → add 5 to both sides → x = 8.

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x−5=3x - 5 = 3
1

The equation

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

x−5=3x - 5 = 3
2

Move the constant

Add 5 to both sides.

x=8x = 8
3

Read the solution

x is already by itself.

x=8x = 8
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.

Add to undo a minus

If x − a = b, then x = b + a (add a to both sides).

Why it works

x − 5 = 3 means x is 5 more than 3.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Solve x - 2 = 5

1

The equation

Solve for x — find the value that makes both sides equal. x - 2 = 5

2

Move the constant

Add 2 to both sides. x = 7

3

Read the solution

x is already by itself. x = 7

EX 2medium

Solve x - 6 = 4

1

The equation

Solve for x — find the value that makes both sides equal. x - 6 = 4

2

Move the constant

Add 6 to both sides. x = 10

3

Read the solution

x is already by itself. x = 10

EX 3hard

Solve x - 4 = 4

1

The equation

Solve for x — find the value that makes both sides equal. x - 4 = 4

2

Move the constant

Add 4 to both sides. x = 8

3

Read the solution

x is already by itself. x = 8

04 / COMMON TRAPS

Where students slip.

Trap

Subtracting instead of adding.

Fix

To undo − 5, add 5.

Trap

Only changing one side.

Fix

Add to 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 - 2 = 5

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
C2

Solve x - 3 = 0

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
C3

Solve x - 9 = -5

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
C4

Solve x - 8 = -6

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
Apply

Apply (4)

A1

Solve x - 9 = -6

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
A2

Solve x - 8 = -1

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
A3

Solve x - 5 = -1

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
A4

Solve x - 6 = 3

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
Extension

Extension (4)

E1

Solve x - 7 = 2

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
E2

Solve x - 7 = -3

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
E3

Solve x - 8 = -5

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.
E4

Solve x - 8 = 4

Need a hint?
  • Add the subtracted number.
  • Do it to both sides.