Scale together
Multiplying or dividing both parts by the same number keeps the ratio the same.
Why it works
2:3 doubled is 4:6.
Ratios · Ratios · 1.3
Equivalent ratios.
Equivalent ratios make the same comparison with bigger or smaller numbers. Multiply (or divide) BOTH parts by the same number. 2:3 = 4:6 = 8:12.
See it work.
Equivalent ratios
Scale both parts together.
Every column is the same ratio as 2:3.
| first | 2 | 4 | 6 | 8 | 10 |
| second | 3 | 6 | 9 | 12 | 15 |
| base | ×2 | ×3 | ×4 | ×5 |
Watch the method
Equivalent ratios
2:3 = ?:12 → ×4 → 8:12, so ? = 8.
1
Find the scale factor
What do you multiply by to get from one ratio to the other? (×4)
2
Scale the other part
Multiply the matching part by the same factor.
Practice until it feels automatic.
Your turn
Work it out.
Type a number, e.g. 40.
streak 0
best 0
… =
The idea underneath.
From easy to tricky.
Find the missing number: 3 : 3 = ? : 6
1
Find the scale factor
What do you multiply by to get from one ratio to the other? (×2) × 2
2
Scale the other part
Multiply the matching part by the same factor. 3:3 = ? :6 => 6
Find the missing number: 2 : 4 = ? : 16
1
Find the scale factor
What do you multiply by to get from one ratio to the other? (×4) × 4
2
Scale the other part
Multiply the matching part by the same factor. 2:4 = ? :16 => 8
Find the missing number: 6 : 2 = ? : 8
1
Find the scale factor
What do you multiply by to get from one ratio to the other? (×4) × 4
2
Scale the other part
Multiply the matching part by the same factor. 6:2 = ? :8 => 24
Where students slip.
Trap
Scaling only one part.
Fix
Multiply BOTH parts by the same number.
Trap
Adding instead of multiplying.
Fix
Equivalent ratios come from multiplying.
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
Find the missing number: 4 : 5 = ? : 15
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
C2
Find the missing number: 3 : 5 = ? : 25
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
C3
Find the missing number: 3 : 5 = 9 : ?
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
C4
Find the missing number: 6 : 6 = ? : 36
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
Apply
Apply (4)
A1
Find the missing number: 1 : 5 = 2 : ?
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
A2
Find the missing number: 5 : 1 = 30 : ?
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
A3
Find the missing number: 3 : 6 = 12 : ?
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
A4
Find the missing number: 1 : 3 = ? : 9
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
Extension
Extension (4)
E1
Find the missing number: 5 : 5 = ? : 20
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
E2
Find the missing number: 5 : 2 = 20 : ?
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
E3
Find the missing number: 1 : 5 = 5 : ?
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.
E4
Find the missing number: 6 : 4 = 12 : ?
Need a hint?
- Find the scale factor between the known parts.
- Apply it to the other part.