Expected Value

I have stuck in a problem ........ Please help me....The problem is ............

A box contains 25 balls which are numbered from 11 to 2525. I took a ball.What is the expected number that the ball have?

Note by Kiriti Mukherjee
6 years, 3 months ago

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The answer is 1313. [provided that all the balls have an equal chance of being selected]

The expected value of a random variable is the weighted average of all possible outcomes.

In your example the probability of a ball being selected is 125\frac{1}{25}. So the expected value would be:

1(125)+2(125)+3(125)+4(125)++23(125)+24(125)+25(125)1(\frac{1}{25})+2(\frac{1}{25})+3(\frac{1}{25})+4(\frac{1}{25})+\cdots + 23(\frac{1}{25})+ 24(\frac{1}{25})+25(\frac{1}{25})

=13=13.

Hope this helps!

Mursalin Habib - 6 years, 3 months ago

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You might want to read this: Expected Value | Brilliant

Tim Vermeulen - 6 years, 3 months ago

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Something's terribly wrong with your link. It redirects me to this page again.

You probably wanted to post this link.

Mursalin Habib - 6 years, 3 months ago

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Thanks for pointing that out, I've updated it.

Tim Vermeulen - 6 years, 3 months ago

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If I choose a ball again with out replace the first ball .What is the expected value of the second ball?

Kiriti Mukherjee - 6 years, 3 months ago

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We are not here to solve problems for you. Mursalin H. told you how to solve the first problem, and if you understand it completely, you should be able to solve this one yourself. I have also provided you with the Brilliant post about the expected value, which will help you understand the concept.

Tim Vermeulen - 6 years, 3 months ago

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Just call me Mursalin. Mursalin H. sounds really odd! :)

Mursalin Habib - 6 years, 3 months ago

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wen all are equiprobable how can one of them(13) have more chances of appearing

Naga Teja - 6 years, 3 months ago

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