Re: Duplicated output with no condition (easy one)

>ls -ltr|awk 'split($8,a,":");t=t+a[2] END {print t,NR ,t/NR }'

what you have here is three rules whereof two have no explicit action.
That is equivalent to:

	ls -ltr|awk 'split($8,a,":") {print} \
                               t=t+a[2] {print} \
                               END {print t,NR ,t/NR }'
-- 

Lorenz