Trying to take an average using INDEX and/or MATCH

A B C
100 32.5 101
100 33.4
100 34.5
100 31.6
100 34.9
101 38.4
101 34.4
101 39.7
101 39.1
101 31.1
102 32.4
102 34.1
102 33.3
102 34.9

I am trying to create a function that will take the value in column C and search column A. Once it finds all matching results, I would like it take an average of the corresponding values in column B.

I have tried =AVERAGE(INDEX(B2:B15,MATCH(C2,A2:A15,0))) and haven't been able to get the correct results.

Try:

=SUMIF($A$2:$A$15,C2,$B$2:$B$15)/COUNTIF($A$2:$A$15,C2)

or

=AVERAGE(IF($A$2:$A$15=C2,$B$2:$B$15))

which must be confirmed with CTRL+SHIFT+ENTER not just ENTER