Probability of occurence: if 1 attempt in 10 succeeds, ....

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If 1 in 10 attemts succed, what is the probability that out of 25 attempts, 2 or more will succeed?
 
Re: Probability of occurence

akirablaid said:
If 1 in 10 attemts succed, what is the probability that out of 25 attempts, 2 or more will succeed?
The probability of no successes in 25 is (0.9)25\displaystyle \left( {0.9} \right)^{25}.
The probability of exactly one success in 25 is (25)(0.1)(0.9)24\displaystyle \left( {25} \right)\left( {0.1} \right)\left( {0.9} \right)^{24}.
Thus the of two or more successes in 25 is 1[(0.9)25+(25)(0.1)(0.9)24]\displaystyle 1 - \left[ {\left( {0.9} \right)^{25} + \left( {25} \right)\left( {0.1} \right)\left( {0.9} \right)^{24} } \right]
 
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