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Perl, 24 + 4 = 28 bytes

$^+=$_/2 for@F;$_=$^~~@F

Requires -paX flags to run, prints 1 as True and nothing as False:

$ perl -paXe'$^+=$_/2 for@F;$_=$^~~@F' <<< '5 3 7'
$ perl -paXe'$^+=$_/2 for@F;$_=$^~~@F' <<< '5 3 8'
1

Perl, 24 + 4 = 28 bytes

$^+=$_/2 for@F;$_=$^~~@F

Requires -paX flags to run, prints 1 as True and nothing as False:

-X disables all warnings.

$ perl -paXe'$^+=$_/2 for@F;$_=$^~~@F' <<< '5 3 7'
$ perl -paXe'$^+=$_/2 for@F;$_=$^~~@F' <<< '5 3 8'
1

Perl, 31 + 3 = 34 bytes

$s+=$_ for@F;$_=grep$s/2eq$_,@F

Requires -pa flags to run, prints a truly value (1 or 2) and a falsy value (0):

$ perl -pae'$s+=$_ for@F;$_=grep$s/2eq$_,@F' <<< '5 3 7'
0
$ perl -pae'$s+=$_ for@F;$_=grep$s/2eq$_,@F' <<< '5 3 8'
1

Smartmatch can also be used if STDERR is ignored (24 + 3 = 27 bytes):

$^+=$_/2 for@F;$_=$^~~@F

$ perl -pae'$^+=$_/2 for@F;$_=$^~~@F' <<< '10 6 4'
Smartmatch is experimental at -e line 1.
1

Perl, 24 + 4 = 28 bytes

$^+=$_/2 for@F;$_=$^~~@F

Requires -paX flags to run, prints 1 as True and nothing as False:

$ perl -paXe'$^+=$_/2 for@F;$_=$^~~@F' <<< '5 3 7'
$ perl -paXe'$^+=$_/2 for@F;$_=$^~~@F' <<< '5 3 8'
1

Perl, 31 + 3 = 34 bytes

$s+=$_ for@F;$_=grep$s/2eq$_,@F

Requires -pa flags to run, prints a truly value (1 or 2) and a falsy value (0):

$ perl -pae'$s+=$_ for@F;$_=grep$s/2eq$_,@F' <<< '5 3 7'
0
$ perl -pae'$s+=$_ for@F;$_=grep$s/2eq$_,@F' <<< '5 3 8'
1

Perl, 31 + 3 = 34 bytes

$s+=$_ for@F;$_=grep$s/2eq$_,@F

Requires -pa flags to run, prints a truly value (1 or 2) and a falsy value (0):

$ perl -pae'$s+=$_ for@F;$_=grep$s/2eq$_,@F' <<< '5 3 7'
0
$ perl -pae'$s+=$_ for@F;$_=grep$s/2eq$_,@F' <<< '5 3 8'
1

Smartmatch can also be used if STDERR is ignored (24 + 3 = 27 bytes):

$^+=$_/2 for@F;$_=$^~~@F

$ perl -pae'$^+=$_/2 for@F;$_=$^~~@F' <<< '10 6 4'
Smartmatch is experimental at -e line 1.
1