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Recall that there are 4 suits - spades, hearts, clubs, and diamonds - in a standard deck
of playing cards. Suppose you play a game in which you draw a card, record the suit,
replace it, shuffle, and repeat until you have observed 10 cards. Define X = numbers of spades observed.
Find the probability of observing 3 or fewer spades in this game. Round to three decimal places.
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In this game, there are 4 suits, and every suit has the same number of card, 13,
so the total number of cards in a standard deck is 4*13 = 52.
At each step, this game returns us to the same initial condition, due to replacing and
shuffling the cards.
Therefore, this game is a typical binomial experiment. At each trial, we have a spade
with the probability 1/4 = 0.25 or any other suit card with the probability 3/4 = 0.75.
So, they want you calculate the probability of having success (having a spade) 3 or fever
times of 10 trials.
Use the standard formula for the binomial probability
P(X <= 3) = P(0) + P(1) + P(2) + P(3)
where P(k) = , are binomial coefficients = .
Now calculate using a calculator
P(0) = = = 0.056313515;
P(1) = = = 0.187711716;
P(2) = = = 0.281567574;
P(3) = = = 0.250282288.
Finally, add the number and get
P(X <= 3) = 0.056313515 + 0.187711716 + 0.281567574 + 0.250282288 = 0.775875092.
Round it to 3 decimals. So, P(X <= 3) = 0.776 (rounded). ANSWER
You may check this result by using a convenient online binomial calculator at
https://stattrek.com/online-calculator/binomial.aspx
At this point, the problem is solved completely.