Taking 100 shots, 70 from 2-pt and 30 from 3-pt. If the 2-pointers are shot at 50% (35/70) and the 3-pointers at 40% (12/30), that would be:
Treating the 2- and 3-pointers equally, you have 35+12 = 47 shots made out of 100, or 47%.
But using the formula eFG% = (1.5*3FGM + FGM) / FGA, you get:
(1.5x12=18) + 35 = 53 shots made out of 100, or 53% effective shooting.
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Now, if that same team stepped back behind the arch on 10 of their 2-pointers to make them 3-pointers, and keeping the same percentages (50% for 2-ptrs and 40% for 3-ptrs) they are now shooting 30/60 for 2-ptrs and 16/40 for 3-ptrs, which works out to:
30 + 16 = 46 out of 100, for 46%.
(1.5x16=24) + 30 = 54 out of 100, for 54% effective shooting.
So, you can see that while their "real" percentage declined when they took more shots from behind the arch while maintaining the same accuracy, their effective shooting percentage increased.
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In terms of points, the first set goes:
35 * 2 points = 70 points, and 12 * 3 points for 36 points, for a total of 106 points.
The second set goes:
30 * 2 points = 60 points, and 16 * 3 points for 48 points, for a total of 108 points.