Student or Learner
Which of these is correct, when expressing money as a numeric value?
£100 worth of free software
£100's worth of free software
£100' worth of free software
You often see these on computer retailers' sites and it is interesting to know which is grammatically correct.
Version 1. £100 worth of free software
I would say this is wrong because there is a possessive relationship between the worth and its value, ie a worth of £100. Therefore an apostrophe is required to indicate possession.
Version 2. £100' worth of free software
This could be the answer. Or could it? £100 represents the words 'one hundred pounds' (pounds being plural) and that's how we say it. However in its numeric form, £100 doesn't end in an s, it ends in a zero, so it looks wrong and probably is wrong to use a plural possessive form. Even if the numeric form with the 0 is plural, if one uses 100' worth it would be confused with the notation for 100 feet. So it would be permissible to use "£100's" even if £100 is deemed to be plural, to clearly indicate possession.
Version 3. £100's worth of free software
£100 is a numeric value and is here expressed in numbers. As such it is not obliged to take plural form because It is a singular entity - a worth of £100 - and therefore does not require a plural possessive form.
I would therefore argue version 3 is correct.
There are many in the UK who use "£100 worth of free software". I've tried to set out arguments for and against in another post. I would argue that people tend not to say, for example, "one pound worth of sweets" - they say "one pound's worth". So there would appear to be a possessive relationship between the worth and what its monetary value is. The question is how to indicate that relationship in a form that's grammatically sound.