convert in ImageMagick resize by percent

#!/bin/bash

image="/media/C/1.jpg"
result="/media/C/12.jpg"
width=`convert $image -format "%w" info:`
height=`convert $image -format "%h" info:`

#Now convert your percentages to pixels as variables, for example

xoff=`convert xc: -format "%[fx:$width*10/100]" info:`
yoff=`convert xc: -format "%[fx:$height*10/100]" info:`
ww=`convert xc: -format "%[fx:$width*40/100]" info:`
hh=`convert xc: -format "%[fx:$height*40/100]" info:`

#then put that into your crop

convert $image -crop ${ww}x${hh}+${xoff}+${yoff} +repage $result
echo 'done'

above is crop, ref to : http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=17441

the following is resize by percentage:

 ref to : http://www.imagemagick.org/Usage/resize/#percent

  convert dragon.gif    -resize 50%  half_dragon.gif
  convert terminal.gif  -resize 50%  half_terminal.gif

such simple ,but i have done it in hard way to finish this percentage resize task..... :-(