Which of these is grammatically correct:

A - I lost one of my friend’s phone number


B - I lost one of my friends’ phone number

They appeared on a grammar test in a classroom, and the teacher said that A was the correct answer. Is the teacher right or wrong, and why?

  • Hello Mark, I suggest looking up plurals and the possessive apostrophe's bearing on this. Commented Sep 27, 2019 at 15:34
  • 1
    They’re both wrong to me. Correct might be one of: 1. “I lost my friend’s phone number” 2. “I lost one of my friend’s phone numbers” 3. “I lost one of my friends’ phone numbers.” In 1. I can’t call my friend at all now. In 2. I’ll have to call him on one of his other numbers. And in 3. I had 10 slips of paper each with a phone number of a friend on it. But now I see I’ve only got nine.
    – Jim
    Commented Sep 27, 2019 at 15:50
  • @Jim Your sentence #3 could be reworded as "I lost the phone numbers of one of my friends," which implies that the friend you're referring to has multiple phone numbers, and you lost all of them. The OP's sentence B can be rephrased as "I lost the phone number of one of my friends," which has the (likely) intended implication that the friend has only one number, which you lost. I don't think your #3 is correct. Commented Sep 27, 2019 at 16:03
  • @NuclearWang - B sounds wrong to me without and ’s’. We can discuss what it might mean after an ’s’ is added. :-)
    – Jim
    Commented Sep 27, 2019 at 16:08
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    If used in conversation....nobody will note the distinction. Commented Sep 27, 2019 at 18:33

1 Answer 1


I believe the teacher is incorrect. There are possibly two interpretations of what the author is speaking of:

  1. they had a friend who had several phone numbers, one of which they lost
  2. they have several friends, and lost the phone number for one of them

The clue to the correct interpretation is that phone number is singular rather than plural, indicating the object of the preposition is 'friends' and not 'number'.

Since it is a reference to one of many friends, then it should be the plural possessive form: friends'


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