Fractions · Equivalent fractions · 2.5

Find the missing number.

When two fractions are equivalent and one number is missing, use the multiplier between the denominators (or numerators) to find it.

01 / THE IDEA

See it work.

Watch the method

Find the missing number

1/2 = ?/8: 2 × 4 = 8, so ? = 1 × 4 = 4.

1 / 2
12=?8\frac{1}{2} = \frac{?}{8}
1

How many times bigger?

2 × 4 = 8.

2×4=82\times4=8
2

Multiply top and bottom

Multiply both by 4 so the value stays the same.

12=48\frac{1}{2} = \frac{4}{8}
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.

The missing piece

Find the multiplier from the known denominators (or numerators), then apply it to the other part.

Why it works

The same scaling links both rows.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Write 2/3 with denominator 9.

1

How many times bigger?

3 × 3 = 9. 3\times3=9

2

Multiply top and bottom

Multiply both by 3 so the value stays the same. 2/3 = 6/9

EX 2medium

Write 3/4 with denominator 16.

1

How many times bigger?

4 × 4 = 16. 4\times4=16

2

Multiply top and bottom

Multiply both by 4 so the value stays the same. 3/4 = 12/16

EX 3hard

Write 1/5 with denominator 25.

1

How many times bigger?

5 × 5 = 25. 5\times5=25

2

Multiply top and bottom

Multiply both by 5 so the value stays the same. 1/5 = 5/25

04 / COMMON TRAPS

Where students slip.

Trap

Adding the difference instead of multiplying.

Fix

Use the multiply factor, not the gap.

Trap

Applying the multiplier to the wrong part.

Fix

Use the factor that links the denominators.

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

Write 2/3 with denominator 9.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
C2

Write 1/3 with denominator 9.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
C3

Write 1/3 with denominator 9.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
C4

Write 1/2 with denominator 10.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
Apply

Apply (4)

A1

Write 3/4 with denominator 16.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
A2

Write 2/3 with denominator 6.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
A3

Write 1/2 with denominator 6.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
A4

Write 1/3 with denominator 9.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
Extension

Extension (4)

E1

Write 1/5 with denominator 25.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
E2

Write 3/5 with denominator 10.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
E3

Write 2/3 with denominator 12.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.
E4

Write 1/2 with denominator 8.

Need a hint?
  • Find the multiplier between the bottoms.
  • Apply it to the top.