In general you have to play all lines to get full pay. If you try to play, for example, five coins on a three line machine, you'll be playing two coins each on the first two lines and one on the third line.
The exception I've seen is on Super Times Pay machines where you can choose to play just one line and play six coins for full play.
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Does the paytable change on multiline games if you only play one line?
We are going to be in Lousiana this weekend and Inoticed that they
ahve a large number of 3/5 play JoB at the $0.25 level. Is it
possible to play just one line and still have the game be full pay?