A ratio compares two amounts. If a class has 12 cats and 18 dogs as pets, the ratio of cats to dogs is 12 : 18, read as twelve to eighteen. The order matters: dogs to cats would be 18 : 12.
Ratios can be simplified like fractions. Divide both parts by the same number. 12 and 18 can both be divided by 6, so 12 : 18 = 2 : 3. This means for every 2 cats there are 3 dogs. A ratio is in simplest form when no number except 1 divides both parts.
Worked example
Write 20 : 35 in its simplest form.
- Both numbers are in the 5 times table.
- 20 ÷ 5 = 4 and 35 ÷ 5 = 7.
Answer:4 : 7
Key words
- ratio
- a comparison of two amounts, written a : b
- simplest form
- the smallest whole numbers with the same ratio
- for every
- how ratios are said in words
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Common Core-referenced: 6.RP.A.1