Each of these 3 maps has base 9% chance of being randomly selected.
A player's choice increases base chance by 3% for that map.
Players who don't make a choice increase base chance of all 3 maps by 1%.
This would ensure all maps sometimes come up.
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Here are the chances of Maps (A, B, C) being selected in the following situations:
All players pick A
A: 81%
B: 9%
C: 9%
Half of players pick A, others make no pick
A: 57%
B: 21%
C: 21%
Half of players pick A, rest pick B
A: 45%
B: 45%
C: 9%
One third of players pick A, B and C each
A: 33%
B: 33%
C: 33%
etc
(The leftover 1% has been removed for ease of illustration, it's actually 9.33% base chance of being selected, etc)
Edited by Talorien, 07 November 2015 - 10:34 PM.