# [SOLVED] Probability of an event occuring 2 out of 4 times

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• Mar 25th 2009, 05:38 PM
jjs2168
[SOLVED] Probability of an event occuring 2 out of 4 times
i have an event that i have calculated the probability to be .0017

what is the probability that this event happens exactly 2 out of 4 times? (assume independence)
• Mar 25th 2009, 05:45 PM
Plato
Quote:

Originally Posted by jjs2168
i have an event that i have calculated the probability to be .0017 what is the probability that this event happens exactly 2 out of 4 times? (assume independence)

Exactly twice: ${4 \choose 2} (.0017)^2(1-.0017)^2$.