The following two phrases are equivalent:
1. mother of Susan
2. Susan's mother

But so are the following:
1. ten years of experience
2. ten years' experience

Can anyone explain why the order of the two terms is
different in the two cases?
1 2
good question! I dont know the answer tho, sorry
Could it be: ten-years experience? as in two-year-old boy.
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The apostrophe means that a word is potentially missing. Susan's mother means "Susan, her mother" (or, the mother of Susan)

"Ten years' experience" means "Ten years, their experience"

We would never actually say 'Ten years, their experience', but is simply a way of explaining the apostrophe here. Emotion: smile
Abbie, this phrase is sort of "illogical", because experience in this case would belong to ten years, but in fact it belongs to the person who has the experience.
Good point Latin. maybe it doesn't need an apostrophe at all!! Emotion: embarrassed
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Experience of ten years = ten years' experience

Mother of Susan = Susan's mother
The apostrophe in "Susan's mother" is showing ownership. The apostrophe in "ten years' experience" makes years both plural and posessive. There are 10 years (plural) and the years refer to the experience (posessive).
I believe the apostrophe is a substitution for "of". In other words, "Ten years of experience" becomes "Ten years' experience."
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