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I googled it but didn't get a result. Such as in one on one lesson. Thank you for your help.

marked as duplicate by J. Taylor, choster, Cascabel, Davo, Mari-Lou A Feb 22 at 8:11

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    Welcome to EL&U. 1:1 is conventionally read as "one to one," not "one on one" which is a different concept. See How do I pronounce “ratio 1:1”? – choster Feb 19 at 1:36
  • 2
    1:1 one to one. 1:2 one to two. 1:3 one to three. Assuming you mean ratios or proportions. – GEdgar Feb 19 at 2:01
  • 1
    .. or odds, or probabilities, or ... – John Lawler Feb 19 at 3:13
  • @JohnLawler Probabilities would actually be between 0 to 1, inclusive. These are odds. – jimm101 Feb 19 at 13:26

As pointed out in comments, the options using colons are normally read as a ratio using the word "to" compare the numbers (i.e. one to one, one to two etc.). This is the most common usage.

Following from your wording, perhaps you are looking for such a comparison in a competitive sense (like a one on one debate for example). If such is the case, it could be read as "one against two" or "one against three" etc. This is also a common usage.

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