Algebra 10
2 marks · EasyExplain why you need to find a lowest common denominator when adding the following algebraic fractions:
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To add fractions with different denominators, you must rewrite them with a common denominator so the numerators can be combined.
Also accept: Because you cannot add fractions unless they have the same denominator.; You need the same denominator to add the numerators.
Common mistakes: Adding numerators directly; Ignoring denominators
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Marking points
B1 · 1 mark · States that a common denominator is needed.
B2 · 1 mark · Reason: so numerators can be combined / needed for valid addition.
Worked solution
Fractions with different denominators cannot be added directly. We need to rewrite each fraction with the same common denominator to add the numerators together.