50% of girls in class give incorrect responses (9)
I believe the answer is:
misinform
'50% of girls in class give incorrect responses' is the definition.
I can't judge whether this definition defines the answer.
'50% of girls in class give' is the wordplay.
'r0% of' means to take half the letters.
'girls' becomes 'misses' ('miss' can be a synonym of 'girl').
'in class give' becomes 'inform' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'misses' halved is 'mis'.
'mis'+'inform'='MISINFORM'
Can you help me to learn more?
(Other definitions for misinform that I've seen before include "Put on the wrong track" , "Provide with incorrect facts" , "Give incorrect gen to" , "Tell incorrectly" , "Instruct wrongly" .)