Does it mean my ad is shown in the top position 20% of the time?
Does it make any difference if ads are shown across the top of the SERPS? Is that still just position #1?
Also, is there any way of finding out how much I have to pay to get the top slot?
In the column that shows the position of my adwords ad, it makes perfect sense when it says position 1 or 2 or 3. But when it says 1.2, what does that mean?
The decimal figure in the 'Avg. Pos' column is literally the average of your ads position over all its impressions, for whatever date range you're looking at.
So, let's say you are looking at the date range of 'today' and your ad has an average position of 3.3. When you look at your impressions you see that you've had 3 so far.
Well, in each of your 3 impressions your ad is likely to have appeared in a different position. Lets say your ad appeared in the actual positions of 2, then 3, and then 5. If you add up all three of those numbers, then divide by three, you will have the average.
2+3+5 = 10 and 10/3 = 3.3 . Thus 3.3 is your 'Avg. Pos' for the date range of 'today'.
This same principle applies for whatever date range, and number of impressions, you're looking at.
AWA