Cinema seat probability

Calculate the probability of the event that you sit in seats 1 to 30 in the cinema at:
a) seat marked with a prime number
b) seat marked with an even number
c) a seat marked with a number divisible by 3 or 4

Final Answer:

p₁ =  0.3333
p₂ =  0.5
p₃ =  0.5

Step-by-step explanation:

$$\begin{gathered} n=30 \\ p:2,3,5,7,11,13,17,19,23,29 \\ {p}_1=\frac{10}{n}=\frac{10}{30}=0.3333 \end{gathered}$$

$p_2=\frac{n/2}{n}=\frac{30/2}{30}=0.5$

$$\begin{gathered} 1224 \\ {n}_3=n/3+\lceil n/4\rceil -2=30/3+\lceil 30/4\rceil -2=16 \\ {d}_3:36912151821242730 \\ {d}_4:481216202428 \\ {p}_3=\frac{17-2}{n}=\frac{17-2}{30}=0.5 \end{gathered}$$

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