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October 25, 2014

October 25, 2014

Posted by **Liz** on Tuesday, May 7, 2013 at 5:34pm.

- Statistics -
**MathMate**, Tuesday, May 7, 2013 at 8:38pmUse binomial probability because:

probability is known and does not change over the experiment,

outcome is binomial (success or failure),

each step of the experiment is similar,

p=0.25

n=10

P(r)=number of question correct

=nCr(p^r)(1-p)^(n-r)

nCr = binomial coefficient = n!/((n-r)!r!)

P(0)=0.0563 (zero question correct)

P(1)=0.1877 (1 question correct)

Therefore, to get at least 20%, or 2 or more questions correct, we have

P(2+)=1-(P(0)+P(1))

=0.7560

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