Section II 14. An urn has 3 red marbles, 2 white marbles, and 2 blue mar- bles. Marbles are sampled, without replacement, until obtaining a red marble. before finding the first red marble. Let X denote the number of marbles that must be sampled (a) table below. Show that the values of the pmf of X are as given in the xf(x) 3/7 2/7 2 6/35 3 3/35 4 1/35 0. 1

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(b) Compute the expected number of marbles that must be sampled before finding the first red marble.
Transcribed Image Text:(b) Compute the expected number of marbles that must be sampled before finding the first red marble.
### Section II

14. An urn has 3 red marbles, 2 white marbles, and 2 blue marbles. Marbles are sampled, without replacement, until obtaining a red marble. Let \( X \) denote the number of marbles that must be sampled **before** finding the first red marble.

(a) **[Instructor's Note]** Show that the values of the probability mass function (pmf) of \( X \) are as given in the table below.

| \( x \) | \( f(x) \) |
|---------|------------|
| 0       | \( \frac{3}{7} \) |
| 1       | \( \frac{2}{7} \) |
| 2       | \( \frac{6}{35} \) |
| 3       | \( \frac{3}{35} \) |
| 4       | \( \frac{1}{35} \) |
Transcribed Image Text:### Section II 14. An urn has 3 red marbles, 2 white marbles, and 2 blue marbles. Marbles are sampled, without replacement, until obtaining a red marble. Let \( X \) denote the number of marbles that must be sampled **before** finding the first red marble. (a) **[Instructor's Note]** Show that the values of the probability mass function (pmf) of \( X \) are as given in the table below. | \( x \) | \( f(x) \) | |---------|------------| | 0 | \( \frac{3}{7} \) | | 1 | \( \frac{2}{7} \) | | 2 | \( \frac{6}{35} \) | | 3 | \( \frac{3}{35} \) | | 4 | \( \frac{1}{35} \) |
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