Math Problem Statement

You are playing a game where you draw a card from a standard deck, and you will win $5 if you draw a face card, $4 if you draw an ace, and lose $6 if you draw any other card. What is the expected gain from this game?

Solution

Let's solve this problem step by step.

The problem asks for the expected gain from a game where:

  • You win $5 if you draw a face card,
  • You win $4 if you draw an ace,
  • You lose $6 if you draw any other card.

Understanding the deck:

  • A standard deck of cards has 52 cards.
  • There are 12 face cards (4 Jacks, 4 Queens, 4 Kings).
  • There are 4 aces.
  • The remaining 36 cards are non-face and non-ace cards.

Assigning probabilities:

  • Probability of drawing a face card: P(face card)=1252P(\text{face card}) = \frac{12}{52}
  • Probability of drawing an ace: P(ace)=452P(\text{ace}) = \frac{4}{52}
  • Probability of drawing any other card: P(other)=3652P(\text{other}) = \frac{36}{52}

Calculating expected gain:

The expected value (E) is calculated using the formula:

E=(gain from face card×P(face card))+(gain from ace×P(ace))+(loss from other cards×P(other))E = (\text{gain from face card} \times P(\text{face card})) + (\text{gain from ace} \times P(\text{ace})) + (\text{loss from other cards} \times P(\text{other}))

Substituting the values: E=(5×1252)+(4×452)+(6×3652)E = (5 \times \frac{12}{52}) + (4 \times \frac{4}{52}) + (-6 \times \frac{36}{52})

Now, calculating each term:

  • 5×1252=60521.155 \times \frac{12}{52} = \frac{60}{52} \approx 1.15
  • 4×452=16520.314 \times \frac{4}{52} = \frac{16}{52} \approx 0.31
  • 6×3652=216524.15-6 \times \frac{36}{52} = \frac{-216}{52} \approx -4.15

Adding these together:

E1.15+0.314.15=2.69E \approx 1.15 + 0.31 - 4.15 = -2.69

The expected gain from the game is approximately -2.69. This means that, on average, you lose $2.69 per game.

Do you want further clarification or details on this calculation?

Here are 5 related questions you can try:

  1. What is the expected value if the loss for any other card is changed to $5?
  2. How does the expected value change if you add another face card?
  3. What is the probability of not losing any money?
  4. If you win $6 for an ace instead of $4, what will be the new expected value?
  5. How would the calculation change if the deck had jokers?

Tip: Always break down the problem into probabilities and corresponding outcomes before computing the expected value.

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Math Problem Analysis

Mathematical Concepts

Probability
Expected Value
Combinatorics

Formulas

E = (gain from event 1 × P(event 1)) + (gain from event 2 × P(event 2)) + (loss from event 3 × P(event 3))
P(face card) = 12/52
P(ace) = 4/52
P(other card) = 36/52

Theorems

Law of Total Probability

Suitable Grade Level

Grades 10-12