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**jacks****Member**- Registered: 2012-11-21
- Posts: 80

A fair dice is rolled . the probability that the first time one occur at even no. of trails

Can any one explain me using Tree Diagram.

Thanks

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,469

hi jacks,

You may throw a one straight away, or on throw 2, or on throw 3, or on throw 4, or ...........

See diagram.

P(one at first throw) = 1/6

P(one at second throw) = 5/6 times 1/6 = 5/36

P(one at third throw) = 5/6 x 5/6 x 1/6 = 25/216

etc etc.

As this goes on for ever you need to know how to do the sum to infinity of a geometric progression. Post again if you want help with that.

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,608

Hi jacks

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

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