взятые по два и т.п.
• There are only four possible sums of digits taken two at a time: 0 plus 0, 1 plus 0, 0 plus 1, and 1 + 1.
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Русско-английский научно-технический словарь
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• There are only four possible sums of digits taken two at a time: 0 plus 0, 1 plus 0, 0 plus 1, and 1 + 1.