Answer:
E[N] = 1
Step-by-step explanation:
Here is the hint we are given on this problem - " Write N = [tex]1_{A_1}[/tex] + [tex]1_{A_2}[/tex] + · · · + [tex]1_{A_{ 13}[/tex]where [tex]A_k[/tex] is the event that a match occurs on deal k. "
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Now the standard thing is to do is let [tex]X_i[/tex] = 1, if there is a match on the [tex]i[/tex]-th pick and 0 otherwise. The number of matches is given to be [tex]X_1[/tex] + [tex]X_2[/tex] . . . + [tex]X_{13}[/tex]. Knowing that, we can use the linearity of expectation -
There are 13 cards and for [tex]i[/tex]-th pick, the probability of having a card with [tex]i[/tex] number is 1 / 13. Therefore, E[N] = E[[tex]X_1[/tex] + [tex]X_2[/tex] . . . + [tex]X_{13}[/tex]] = 1
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Solution: E[N] = 1
