Foundation and Higher · ratio notation
Writing and
simplifying ratios.
order matters,
units must match
a ratio compares amounts —
6 : 4
read it as “6 to 4”
the order follows the words
step 1 of 4
Write the ratio
1. Red is said first, so red goes first.
2. Divide both sides by the same number.
✓ 3 : 2. Writing 2 : 3 would be wrong
6 red counters, 4 white
red : white
step 2 of 4
Simplify fully
1. Keep dividing until nothing else goes.
2. The HCF of 18 and 24 is 6.
✓ Same as simplifying a fraction
18 : 24
= 9 : 12 ÷ 2
= 3 : 4 ÷ 3
or ÷ 6 in one go
step 3 of 4
Match the units
1. Put both amounts in the same unit.
2. Then drop the units and simplify.
✓ 50 : 2 would be wrong
50p : £2
= 50 : 200 both in pence
= 1 : 4
step 4 of 4
The form 1 : n
1. Divide both sides by the first number.
2. Decimals are allowed in the form 1 : n.
✓ Otherwise, multiply to clear decimals
4 : 10 write as 1 : n
= 1 : 2.5 ÷ 4
1.5 : 2 = 3 : 4 × 2
ratios —
Units
the same on both sides
Simplify
divide both by the same number
Whatever you do to one side,
do to the other.
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