Answer:
If you take into account all probabilities, and work on a strategy, rather than individual guesses, you can increase the probability.
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Here are the possible outcomes:
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BBB
BBR
BRB
BRR
RBB
RBR
RRB
RRR
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If you use the strategy:
If a person sees a blue and a red, they pass;
If a person sees a blue and a blue, they guess red;
If a person sees a red and a red, they guess blue;
The probability comes out like this:
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(B=blue, R=red, P=pass)
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actual  guess  correct?
BBB RRR no
BBR PPR yes
BRB PRP yes
BRR BPP yes
RBB RPP yes
RBR PBP yes
RRB PPB yes
RRR BBB no
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As you can see, this is a 6/8, or 75% chance of being correct.