01 / THE IDEA

See it work.

Watch the method

Subtract with the LCD

5/6 − 1/4: LCD 12 → 10/12 − 3/12 = 7/12.

1 / 3

\frac{5}{6} - \frac{1}{4}

1

Find the LCD

The least common denominator of 6 and 4 is 12.

\text{LCD}(6,4)=12

2

Rewrite each fraction

Give both the LCD.

\frac{10}{12} - \frac{3}{12}

3

Subtract the numerators

Keep the LCD.

\frac{7}{12}

02 / YOUR TURN

Practice until it feels automatic.

Your turn

Work it out.

Type a fraction like 3/4 or 1 1/2.

streak 0

best 0

… =

— / WHY IT WORKS

The idea underneath.

Common pieces

Over the LCD the pieces match, so subtraction is just subtracting numerators.

Why it works

Same-size pieces make the take-away clean.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Subtract 3/4 - 1/3

1

Find the LCD

The least common denominator of 4 and 3 is 12. \text{LCD}(4,3)=12

2

Rewrite each fraction

Give both the LCD. 9/12 - 4/12

3

Subtract the numerators

Keep the LCD. 5/12

EX 2medium

Subtract 2/3 - 1/4

1

Find the LCD

The least common denominator of 3 and 4 is 12. \text{LCD}(3,4)=12

2

Rewrite each fraction

Give both the LCD. 8/12 - 3/12

3

Subtract the numerators

Keep the LCD. 5/12

EX 3hard

Subtract 5/6 - 2/3

1

Find the LCD

The least common denominator of 6 and 3 is 6. \text{LCD}(6,3)=6

2

Rewrite each fraction

Give both the LCD. 5/6 - 4/6

3

Subtract the numerators

Keep the LCD. 1/6

04 / COMMON TRAPS

Where students slip.

Trap

Subtracting tops over different bottoms.

Fix

Make the denominators match first.

Trap

LCD errors.

Fix

Use the smallest common multiple.

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

Subtract 3/4 - 1/3

Need a hint?

Find the LCD.
Rewrite both, then subtract.

C2

Subtract 5/6 - 3/4

Need a hint?

Find the LCD.
Rewrite both, then subtract.

C3

Subtract 2/3 - 1/4

Need a hint?

Find the LCD.
Rewrite both, then subtract.

C4

Subtract 3/4 - 1/3

Need a hint?

Find the LCD.
Rewrite both, then subtract.

Apply

Apply (4)

A1

Subtract 2/3 - 1/4

Need a hint?

Find the LCD.
Rewrite both, then subtract.

A2

Subtract 5/6 - 1/4

Need a hint?

Find the LCD.
Rewrite both, then subtract.

A3

Subtract 2/3 - 2/4

Need a hint?

Find the LCD.
Rewrite both, then subtract.

A4

Subtract 5/6 - 1/3

Need a hint?

Find the LCD.
Rewrite both, then subtract.

Extension

Extension (4)

E1

Subtract 5/6 - 2/3

Need a hint?

Find the LCD.
Rewrite both, then subtract.

E2

Subtract 3/4 - 1/3

Need a hint?

Find the LCD.
Rewrite both, then subtract.

E3

Subtract 5/6 - 2/3

Need a hint?

Find the LCD.
Rewrite both, then subtract.

E4

Subtract 3/4 - 2/3

Need a hint?

Find the LCD.
Rewrite both, then subtract.

Subtract with the LCD.