At the end of the first quarter, the winning team had double the points of the losing team, meaning the winning team had already scored 10*2=<<10*2=20>>20 points.
At the end of the second quarter, the winning team had 10 more points than it started with, a total of 20+10=30 points.
At the end of the third quarter, the winning team had 20 more points than the number it had in the second quarter, a total of 20+30=<<20+30=50>>50 points.
If the total points the winning team scored in the game was 80, they scored 80-50=<<80-50=30>>30 points in the fourth quarter.
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