'Two years and a half' is an error commonly made by Spanish speakers. You will hear English speakers make the converse mistake in Spanish sometimes... dos y medio años. Both sound terrible.
2017年12月14日
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Two and a half years
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two and a half years.
2017年12月14日
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I don't think I've heard many people at all say "two years and a half". Almost everyone I know would say "Two and a half years".