Primary 2 Fractions
Make equal parts of one whole, write and compare fractions, then add or subtract parts with the same denominator.
Numerator and denominator
A fraction tells us how many equal parts of one whole we are counting. In the example below, the whole is divided into four equal parts and three are shaded.
Numerator: 3 is the top number. It tells us how many parts are being counted.
Denominator: 4 is the bottom number. It tells us how many equal parts make one whole.
Common mistake: Swapping the two numbers. First count all the equal parts in the whole for the denominator, then count the parts named in the question for the numerator.
Fraction of a whole: equal parts
Before naming a fraction, check that the whole is divided into equal parts. Unequal pieces cannot be counted as fourths, even if there are four of them.
Write the shaded part as a fraction
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Check that all four parts are equal. How many parts make the whole?
Common mistake: Calling four unequal pieces fourths. A denominator of 4 means four equal parts of the same whole.
Compare fractions of the same whole
Compare fractions using the same-sized whole. If the denominators match, compare the numerators. For unit fractions, more equal parts make each part smaller.
Same denominator: three eighths and five eighths
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Unit fractions: one third and one fourth
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Common mistake: Thinking 14 is greater than 13 because 4 is greater than 3. When the same whole is cut into more equal parts, each part is smaller.
Add and subtract like fractions
Like fractions have the same denominator. Keep that denominator because the size of each part stays the same. Add or subtract only the numerators. These examples stay within one whole, with denominators no greater than 12.
Add eighths
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Subtract twelfths
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Common mistake: Adding or subtracting the denominators too. In 28 + 38, the parts are still eighths, so the denominator stays 8.