sum of more than 1 column

UNIX for Advanced & Expert Users
1

Hi

I want to sum of 3 columns in file.

Example: I want to sum of 3 ,6,8 th columns in file(SUM(3,6,8)).

Using awk can sum of single column

awk '{a+=$3} END {printf ("%f\n",a)' file_name

Thanks inadvance
MR

2 
awk '{a+=$3+$6+$8} END {printf ("%f\n",a)' file_name
3

Hi ,
Thanks for your reply

Thanks
MR