+0
When I did a proofreading ex., I found that the answer is >>in average<<.The sentence is showed below

I would like to congratulate all of you because the 20 km sponsored walk raised much more money this year than last

year.This is because many more students took part this year than last year and each of them was able to get more
in
sponsors on average returns.

Is it right?? in average?? What is the difference between "in average'' & "on average"???
+0
I would like to congratulate all of you because the 20-km sponsored walk raised much more money this year than last
year. This is because many more students took part this year, and each of them was able to get more on average from their sponsors.

Is it right??-- It is right as corrected. The ending of the original sentence is indecipherable.
in average??-- No, not possible here.
What is the difference between "in average'' & "on average"?-- The first is not English in this situation, though I suppose I could construct another kind of sentence in which is is OK: 'In average homes there are 2.5 TV sets'.
Comments  
Students: We have free audio pronunciation exercises.
Next time when I facing the same question,how can I decide to use In/On??
As to your example,In >> average homes<< there are 2.5 TV sets.
Is that "average" is describing the homes?
Yes, 'average' is describing 'homes', and 'in' is just a preposition, not connected particularly with 'average'. On the other hand, 'on average' is a set adverbial phrase, and it will always be set apart with commas from the rest of the sentence.