Calculating the Probability of Picking a 5

Oct 13, 2025 by wbrum.org 16 views

The Probability of Picking Two 5s in a Row

In this article, we will explore the concept of probability and how it applies to a simple card-picking scenario. We will calculate the probability of picking a 5 and then picking another 5 without putting the first card back. This problem is a classic example of conditional probability, where the probability of the second event depends on the outcome of the first event.

Probability is a measure of the likelihood of an event occurring. It is usually expressed as a fraction or a decimal value between 0 and 1. In this case, we want to find the probability of picking a 5 and then picking another 5.

The Sample Space

Let's assume we have a standard deck of 52 cards, consisting of 4 suits (hearts, diamonds, clubs, and spades) with 13 cards in each suit. The sample space is the set of all possible outcomes, which in this case is the set of all 52 cards.

Picking the First Card

When we pick the first card, there are 52 possible outcomes. Since we are interested in picking a 5, we need to count the number of 5s in the deck. There are 4 5s in the deck, one in each suit.

Calculating the Probability of Picking a 5

The probability of picking a 5 on the first draw is the number of 5s divided by the total number of cards:

P(5) = Number of 5s / Total number of cards = 4 / 52 = 1/13

Picking the Second Card

After picking the first card, there are 51 cards left in the deck. Since we did not put the first card back, the probability of picking a 5 on the second draw depends on the outcome of the first draw.

Calculating the Probability of Picking a 5 Given That a 5 Was Picked on the First Draw

If a 5 was picked on the first draw, there are 3 5s left in the deck. The probability of picking a 5 on the second draw is:

P(5|5) = Number of 5s left / Total number of cards left = 3 / 51

Calculating the Probability of Picking a 5 Given That a Non-5 Was Picked on the First Draw

If a non-5 was picked on the first draw, there are still 4 5s in the deck. The probability of picking a 5 on the second draw is:

P(5|non-5) = Number of 5s / Total number of cards = 4 / 51

Calculating the Overall Probability

To calculate the overall probability of picking a 5 and then picking another 5, we need to consider both scenarios: picking a 5 on the first draw and picking a non-5 on the first draw.

P(5 and 5) = P(5) * P(5|5) + P(non-5) * P(5|non-5)

Since P(non-5) = 1 - P(5) = 12/13, we can substitute the values:

P(5 and 5) = (1/13) * (3/51) + (12/13) * (4/51) = 3/663 + 48/663 = 51/663

Simplifying the Fraction

The fraction 51/663 can be simplified by dividing both the numerator and the denominator by their greatest common divisor, which is 3:

P(5 and 5) = 17/221

In conclusion, the probability of picking a 5 and then picking another 5 without putting the first card back is 17/221. This problem is a classic example of conditional probability, where the probability of the second event depends on the outcome of the first event.

The final answer is: 17/221
You Pick a Card at Random: A Q&A on Probability

In our previous article, we explored the concept of probability and how it applies to a simple card-picking scenario. We calculated the probability of picking a 5 and then picking another 5 without putting the first card back. In this article, we will answer some frequently asked questions related to this problem.

Q: What is the probability of picking a 5 on the first draw?

A: The probability of picking a 5 on the first draw is 1/13, since there are 4 5s in a standard deck of 52 cards.

Q: What is the probability of picking a 5 on the second draw if a 5 was picked on the first draw?

A: If a 5 was picked on the first draw, there are 3 5s left in the deck. The probability of picking a 5 on the second draw is 3/51.

Q: What is the probability of picking a 5 on the second draw if a non-5 was picked on the first draw?

A: If a non-5 was picked on the first draw, there are still 4 5s in the deck. The probability of picking a 5 on the second draw is 4/51.

Q: How do we calculate the overall probability of picking a 5 and then picking another 5?

A: To calculate the overall probability, we need to consider both scenarios: picking a 5 on the first draw and picking a non-5 on the first draw. We use the formula:

P(5 and 5) = P(5) * P(5|5) + P(non-5) * P(5|non-5)

Q: What is the overall probability of picking a 5 and then picking another 5?

A: The overall probability of picking a 5 and then picking another 5 is 17/221.

Q: Why is the probability of picking a 5 on the second draw different depending on the outcome of the first draw?

A: The probability of picking a 5 on the second draw depends on the outcome of the first draw because the number of 5s in the deck changes after the first draw. If a 5 was picked on the first draw, there are fewer 5s left in the deck, so the probability of picking a 5 on the second draw is lower.

Q: Can we generalize this problem to other cards or scenarios?

A: Yes, we can generalize this problem to other cards or scenarios. For example, we could calculate the probability of picking a specific suit or a specific rank on the second draw. We would need to adjust the probabilities accordingly based on the specific scenario.

Q: What is the significance of this problem in real-life situations?

A: This problem has significance in real-life situations where we need to make decisions based on probabilities. For example, in finance, we might need to calculate the probability of a stock price increasing or decreasing based on historical data. In medicine, we might need to calculate the probability of a patient responding to a treatment based on their medical history.