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LingakuLingaku差不多 + [quantity] [quantity] + 左右 大概 + [quantity]
差不多, 大概 and 左右 all hedge a number: "about", "around", "or so". 差不多 and 大概 go before the quantity; 左右 goes after it.
左右 attaches only to a quantity – a number, a time, an age, a price. It cannot hedge a verb.
差不多 and 大概 also work without a quantity, and there they part ways. 差不多 says something is nearly the case, or that two things are much the same. 大概 in front of a verb means "probably".
A number plus 多 is another approximation, meaning "and a bit more": 二十多个 is twenty-odd, 一百多块 is a hundred and something.