If the letter "a" is part of your entry, XL interprets the value as
Text, and you can't use number formatting. A helper column could contain:

=TEXT(LEFT(A1,LEN(A1)-1),"000-000-000") & RIGHT(A1,1)


If you just have the number in the cell, and want to display "a" after
it, one way is:

Format/Cells/Number/Custom 000-000-000\a


In article ,
"Greg Brow" wrote:

I have a series of numbers 123456789 and it is followed with a letter a

I need to show on a worksheet in this format 123-456-789a I cant work out
how to set the cell i have tried 000-000-000 but not sure how to get it to
recognise the letter after