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The number of eggs laid on a tree leaf by an insect of a certain type is a Poisson random variable with parameter λ. However, such a random variable can be observed only if it is positive, since if it is 0, then we cannot know that such an insect was on the leaf. If we let Ydenote the observed number of eggs, then

P{Y=i}=P{X=i∣X>0}

where Xis Poisson with parameter λ. Find E[Y].

Short Answer

Expert verified

The value ofEY=λ1-e-λ

Step by step solution

01

Given information

Given in the question that , The number of eggs laid on a tree leaf by an insect of a certain type is a Poisson random variable with parameter λ. However, such a random variable can be observed only if it is positive, since if it is 0 , then we cannot know that such an insect was on the leaf. If we let Ydenote the observed number of eggs, then

P{Y=i}=P{X=i∣X>0}

where Xis Poisson with parameter λ.

02

Explanation

We have,

P(Y=i)=P(X=i∣X>0)=P(X=i)P(X>0)=P(X=i)1-P(X=0)

=11-e-λP(X=i)

Using the definition of expectation, we have that

EY=∑i=1∞iP(Y=i)=11-e-λ∑i=1∞iP(X=i)

=11-e-λ∑i=0∞iP(X=i)=11-e-λEX

=λ1-e-λ

03

Step 3:Final answer

EY=λ1-e-λ

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