Question 1199988
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In a sequence of independent rolls of a fair die, find the probability that
i) The first "3" is observed on the fifth trial
ii) At least 4 trials are required to obtain a "1"
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            In this my post,  I will solve part  (i),   ONLY.



<pre>
Event in part (i) is the intersection of two independent events E and F.


    Event E is that first 4 rolls are "not 3".

    Event F is that the 5-th draw is "3".


Therefore, the probability of event in part (i) is

    P(event in part (i) ) = {{{(5/6)^4*(1/6)}}} = {{{5^4/6^5}}}.    <U>ANSWER</U>
</pre>

Solved.