trimming and binning rows

I could not find this on the search..

I want to know how to trim a row

so lets say I have a file that looks like this:

bob 88888888888888

and I want to trim column 2 (lets say 4 off the front and end)

bob 888888

Also, how would I bin column 2

Lets so I want to add and average every 3 values?

this will remove first 4 and last 4 char of field

awk '{print substr($2,5,length($2)-8)}'

adding and avg can be done with awk