@tanguatlay,
tanguatlay wrote:Do you mean to convey the idea of being part (e.g. half) way though a chapter? E.g. I am half way through the eleventh chapter?
That's what I meant?
As already said, you cannot use ordinal numbers (ending -th etc) to express something involving a fraction. You would use the ordinal for the whole number and a separate phrase for the fractional part like the expression in blue above.
The idea of 'eleventh and a half' is ambiguous. If you mean eleven whole chapters and, in addition, half a chapter, then that places you in the middle of the twelfth chapter. So define carefully exactly what you want to say.