there are 4 categories that are completely exhaustive of every possibility (assuming that favorable and unfavorable are the only ways to vote)
(1) favorable ONLY A (or flip side is you find only B unfavorable)
(2) favorable ONLY B (or flip side is you find only A unfavorable)
(3) favorable BOTH A and B
(4) unfavorable both A and B
Let total # of registered voters = 100
4 categories sum to 100 registered voters
(1) + (2) + (3) + (4) = 100
35% of 100 registered voters = category (4) unfavorable A and B ——> (4) = 35
20% of 100 registered voters = category (1) find ONLY A favorable ——> (1) = 20
20 + (2) + (3) + 35 = 100
(Category 2) + (category 3) = 45
45% of 100 registered fall under either category (2) or (3) ——> 45 registered voters either:
Find ONLY B favorable
OR
Find BOTH A and B favorable
Ratio of:
favorable BOTH : favorable ONLY B = 1k : 2k
1k + 2k = 45 voters
3k = 45 ——-> k = 15
# of registered voters who find BOTH A and B favorable = 15
Total # of registered voters = assumed to be 100
Answer: 15/100 = 15%
A
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