A person decides to tease a neighbor's dog. The dog bites in 30% of cases when people tease it. The person decides to tease the dog no more than 3 times, up to the first bite. $X$ is the number of attempts to tease the dog in which the dog does not bite. We need to create a probability distribution for the random variable $X$.

Probability and StatisticsProbability DistributionRandom VariableGeometric DistributionProbability
2025/4/17

1. Problem Description

A person decides to tease a neighbor's dog. The dog bites in 30% of cases when people tease it. The person decides to tease the dog no more than 3 times, up to the first bite. XX is the number of attempts to tease the dog in which the dog does not bite. We need to create a probability distribution for the random variable XX.

2. Solution Steps

Let pp be the probability of the dog biting, so p=0.3p = 0.3.
Let qq be the probability of the dog not biting, so q=1p=10.3=0.7q = 1 - p = 1 - 0.3 = 0.7.
The random variable XX can take values 0, 1,

2. If $X=0$, it means the dog bites on the first try. The probability is $P(X=0) = p = 0.3$.

If X=1X=1, it means the dog doesn't bite on the first try and bites on the second try. The probability is P(X=1)=qp=0.70.3=0.21P(X=1) = q \cdot p = 0.7 \cdot 0.3 = 0.21.
If X=2X=2, it means the dog doesn't bite on the first and second tries, and bites on the third try. The probability is P(X=2)=qqp=q2p=(0.7)20.3=0.490.3=0.147P(X=2) = q \cdot q \cdot p = q^2 \cdot p = (0.7)^2 \cdot 0.3 = 0.49 \cdot 0.3 = 0.147.
The probability distribution is as follows:
P(X=0)=0.3P(X=0) = 0.3
P(X=1)=0.21P(X=1) = 0.21
P(X=2)=0.147P(X=2) = 0.147
Let's verify that the probabilities sum up to less than or equal to

1. $0.3 + 0.21 + 0.147 = 0.657$. The person stops after the first bite or after 3 tries.

The complement probability is 10.657=0.3431 - 0.657 = 0.343. This probability corresponds to that the dog did not bite after the 3 tries and the person just stopped trying to tease it. However, it is given that the variable XX represent the number of attempts to tease the dog in which the dog does *not* bite.

3. Final Answer

The probability distribution of XX is:
P(X=0)=0.3P(X=0) = 0.3
P(X=1)=0.21P(X=1) = 0.21
P(X=2)=0.147P(X=2) = 0.147

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