how to delete duplicated songs all at one time?

Some how I got duplicates of my library on iTunes and to get rid of all the new duplicates I went to the library I looked for the date the new duplicate songs were added to the library then I went to columns and where you see Artist, song,

bit rate, time, etc and added 'date added' once that's done click on the box enclosing 'date added' and you will see all songs added by date. Proceed to the last one of the songs with that date press command to highlight it then scroll all the way to the first song and press 'shift' to highlight all of the songs added on that date then simply press delete.

you will be asked if you want to delete these songs...That's it.