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Introductory Statistics: Probability, Distributions, and Binomial Experiments – Guided Study Notes

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Q14a. What is the probability that the card selected is either a queen or a black card?

Background

Topic: Probability with a Standard Deck of Cards

This question tests your understanding of the addition rule of probability, especially when events are not mutually exclusive (since a card can be both a queen and a black card).

Key Terms and Formulas

  • Mutually Exclusive Events: Events that cannot happen at the same time.

  • Addition Rule (Not Mutually Exclusive):

  • = Probability of drawing a queen

  • = Probability of drawing a black card

  • = Probability of drawing a card that is both a queen and a black card

Standard deck of cards

Step-by-Step Guidance

  1. Determine the total number of cards in a standard deck (usually 52).

  2. Count the number of queens in the deck and calculate .

  3. Count the number of black cards in the deck and calculate .

  4. Count the number of cards that are both queens and black (i.e., black queens) and calculate .

  5. Set up the addition rule formula for not mutually exclusive events: .

  6. Plug in the values you found for , , and , but do not compute the final probability yet.

Try solving on your own before revealing the answer!

Final Answer: 0.423

There are 4 queens and 26 black cards in a standard deck. Two cards are both black and queens (queen of spades and queen of clubs). Using the formula:

However, rounding to three decimal places, the answer is 0.538.

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