Probability

Question

Answer 1

Audit records per day = 10 million = 10 * 10⁶ = 10⁷

Records reflected by attacks per day = 10 * 20 = 200

Probability of attacks (intrusions) per day = $\frac{200}{10^{7}}$ = 2 * 10^-5

Probability of no intrusions = 1 - 2 * 10^-5 = 0.99998

Using Bayes theorem,

Required probability = $\frac{0.6*2*10^{-5}}{0.6*2*10^{-5} + 0.99998*0.0005}$ = 0.0234

So, only 2.34 % of total alarms correspond to real intrusions.

Comments

@just_bhavana Does time alarm rate refers to alarm when there is an actual intrusion (i.e. P($\frac{A}{R}$))

A= alarm and R = Intrusion

I am confused with this ?

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yes that is a bit ambiguous, they should've mentioned what time-alarm rate means. I did assuming actual intrusion.