Question: Let MM be an algorithm that solves a decision problem so that on every string xx , if xx is a yes instance of ,

Let
MM
be an algorithm that solves a decision problem
so that on every string
xx
,
if
xx
is a yes instance of
, then
MM
returns the answer yes with probability
11
;
if
xx
is a no instance of
, then
MM
returns the answer no with probability
1/31/3
.
Alice, Bob, and Carol want to amplify the success probability of
MM
from
1/31/3
to a higher value
pp
. To this end. they suggest three different algorithms:
Alice suggests the following algorithm
AA
. On a given input
xx
, run
MM
five times. If at least one of the answers is yes, return yes. Otherwise, return no.
Bob suggests the following algorithm
BB
. On a given input
xx
, run
MM
five times. If at least one of the answers is no, return no. Otherwise, return yes.
Carol suggests the following algorithm
CC
. On a given input
xx
, run
MM
five times. If the majority of the answers is yes, return yes. Otherwise, return no.
Questions:
Which of
AA
,
BB
, and
CC
indeed amplifies the probability of success?
What is the new success probability
pp
?

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