(3) Competence without

Competence without willingness yields in a half-hearted result.

  1. Here “in” is used wrongly. I want to know why?
  2. what is the meaning of half-hearted?

‘In’ is not needed with ‘yields’.
‘Yields’ means produces or provides.
We don’t say ‘produces in’ or ‘provides in’.

Competence without willingness yield a half-hearted result.
Competence without willingness produces a half-hearted result.

You’ll find the meaning in a Learner’s Dictionary

You eliminate “s” with the yield. why?

Attaching "in’ to the verb “yield” is similar to attaching “of” to the verb “comprise”, which is a common mistake even among native speakers.

As for the meaning of “half-hearted result”, I think it means “without spirit” or “with little enthusiasm”.

That was a typo, It was only the ‘in’ I meant to eliminate. Sorry:
Competence without willingness yields a half-hearted result.