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Jun 24'24

Exercise

Suppose we have an urn containing 5 yellow balls and 7 green balls. We draw 3 balls, without replacement, from the urn. Find the expected number of yellow balls drawn.

References

Doyle, Peter G. (2006). "Grinstead and Snell's Introduction to Probability" (PDF). Retrieved June 6, 2024.

Jun 26'24

Solution: E

The number of yellows balls drawn has probability distribution:

[[math]] P(N=k) = \frac{\binom{5}{k} \binom{7}{3-k}}{\binom{12}{3}}. [[/math]]

Calculating the above gives:

Probability distribution for the number of yellow balls drawn
k P(N=k)
1 0.4773
2 0.3182
3 0.0455

And therefore the expected value equals:

0.4773 + 0.3182*2 + 0.0455*3 = 1.2502
00