What scale and key are these notes in?

Question

A B D E F# G

from the song Adams Song (blink-182)

Answer 1

It could be several keys depending on the song.

Most likely is G Major (only F#)

Also possible is D Major (F# and C#) but we don't know until you find out if the C is sharp or not.

Easiest way to tell is to figure out if the piece centers around G or D.  

Answer 2

A general rule is the last note in a piece will give you the key.

I am guessing G Major for both the scale and key.

There are a few scales that are rarely used that have fewer than 8 notes.  I doubt if this is one.