# expected value

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• Jun 20th 2011, 11:38 PM
mathmathmathhh
expected value
a garage knows that they have three charged and two dead batteries placed together by mistake. the random variable X is the number of batteries that have to be tested before all batteries are correctly identified as dead or charged.

Use a probability tree to complete the table for the probability function of X.

x= 0, P(X=x)=?

then keep doing it until x reaches five.
• Jun 21st 2011, 01:35 AM
mr fantastic
Re: expected value
Quote:

Originally Posted by mathmathmathhh
a garage knows that they have three charged and two dead batteries placed together by mistake. the random variable X is the number of batteries that have to be tested before all batteries are correctly identified as dead or charged.

Use a probability tree to complete the table for the probability function of X.

x= 0, P(X=x)=?

then keep doing it until x reaches five.

Well, did you draw the tree as instructed? What is the trouble doing that? Now use the tree to calculate the required probabilities. If more help is needed, please show all that you've done and say where exactly you're stuck.