Duplicated output with no condition (easy one)

Hi all,

I drop a quick one-liner awk to get the avg time (minutes) from a ls
command. on AIX 5.2

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

and I get correct values for  t, NR and t/NR, but the output on screen
shows each file twice

ls -ltr
total 5256
-rw-r--r--   1 cofee    domain       216040 Feb 22 03:14
YellowPages20080221.unl
-rw-r--r--   1 cofee    domain       339846 Feb 23 03:22
YellowPages20080222.unl
-rw-r--r--   1 cofee    domain       167007 Feb 24 03:09
YellowPages20080223.unl
-rw-r--r--   1 cofee    domain        13838 Feb 25 03:03
YellowPages20080224.unl
-rw-r--r--   1 cofee    domain       236632 Feb 26 03:18
YellowPages20080225.unl
-rw-r--r--   1 cofee    domain       141790 Feb 27 03:12
YellowPages20080226.unl
-rw-r--r--   1 cofee    domain       111324 Feb 28 03:07
YellowPages20080227.unl
-rw-r--r--   1 cofee    domain       167925 Feb 29 03:16
YellowPages20080228.unl
-rw-r--r--   1 cofee    domain       360033 Mar 01 03:20
YellowPages20080229.unl
-rw-r--r--   1 cofee    domain       163390 Mar 03 03:15
YellowPages20080302.unl
-rw-r--r--   1 cofee    domain       273029 Mar 04 03:19
YellowPages20080303.unl
-rw-r--r--   1 cofee    domain       255694 Mar 05 03:18
YellowPages20080304.unl
-rw-r--r--   1 cofee    domain       226711 Mar 06 03:16
YellowPages20080305.unl

when i drop the command
ls -ltr|awk 'split($8,a,":");t=t+a[2] END {print t,NR ,t/NR }'
-rw-r--r--   1 cofee    domain       216040 Feb 22 03:14
YellowPages20080221.unl
-rw-r--r--   1 cofee    domain       216040 Feb 22 03:14
YellowPages20080221.unl
-rw-r--r--   1 cofee    domain       339846 Feb 23 03:22
YellowPages20080222.unl
-rw-r--r--   1 cofee    domain       339846 Feb 23 03:22
YellowPages20080222.unl
-rw-r--r--   1 cofee    domain       167007 Feb 24 03:09
YellowPages20080223.unl
-rw-r--r--   1 cofee    domain       167007 Feb 24 03:09
YellowPages20080223.unl
-rw-r--r--   1 cofee    domain        13838 Feb 25 03:03
YellowPages20080224.unl
-rw-r--r--   1 cofee    domain        13838 Feb 25 03:03
YellowPages20080224.unl
-rw-r--r--   1 cofee    domain       236632 Feb 26 03:18
YellowPages20080225.unl
-rw-r--r--   1 cofee    domain       236632 Feb 26 03:18
YellowPages20080225.unl
-rw-r--r--   1 cofee    domain       141790 Feb 27 03:12
YellowPages20080226.unl
-rw-r--r--   1 cofee    domain       141790 Feb 27 03:12
YellowPages20080226.unl
-rw-r--r--   1 cofee    domain       111324 Feb 28 03:07
YellowPages20080227.unl
-rw-r--r--   1 cofee    domain       111324 Feb 28 03:07
YellowPages20080227.unl
-rw-r--r--   1 cofee    domain       167925 Feb 29 03:16
YellowPages20080228.unl
-rw-r--r--   1 cofee    domain       167925 Feb 29 03:16
YellowPages20080228.unl
-rw-r--r--   1 cofee    domain       360033 Mar 01 03:20
YellowPages20080229.unl
-rw-r--r--   1 cofee    domain       360033 Mar 01 03:20
YellowPages20080229.unl
-rw-r--r--   1 cofee    domain       163390 Mar 03 03:15
YellowPages20080302.unl
-rw-r--r--   1 cofee    domain       163390 Mar 03 03:15
YellowPages20080302.unl
-rw-r--r--   1 cofee    domain       273029 Mar 04 03:19
YellowPages20080303.unl
-rw-r--r--   1 cofee    domain       273029 Mar 04 03:19
YellowPages20080303.unl
-rw-r--r--   1 cofee    domain       255694 Mar 05 03:18
YellowPages20080304.unl
-rw-r--r--   1 cofee    domain       255694 Mar 05 03:18
YellowPages20080304.unl
-rw-r--r--   1 cofee    domain       226711 Mar 06 03:16
YellowPages20080305.unl
-rw-r--r--   1 cofee    domain       226711 Mar 06 03:16
YellowPages20080305.unl
189 14 13.5