Math Problem Statement

On a rainy day, 90% of the students on a campus of 10,000 students are carrying umbrellas. Two students walk into a classroom on this campus. What is the probability that at least one of them is not carrying an umbrella?

Solution

The problem in the image is as follows:

On a rainy day, 90% of the students on a campus of 10,000 students are carrying umbrellas. Two students walk into a classroom. What is the probability that at least one of them is not carrying an umbrella?

Let's break it down step by step:

  1. Probability that a student is carrying an umbrella = 90% = 0.9
  2. Probability that a student is not carrying an umbrella = 1 - 0.9 = 0.1

Now, we need to calculate the probability that at least one of the two students is not carrying an umbrella. To do this, we can first calculate the probability that both students are carrying umbrellas, and subtract this from 1.

  • Probability that both students are carrying umbrellas = 0.9×0.9=0.810.9 \times 0.9 = 0.81
  • Probability that at least one of them is not carrying an umbrella = 10.81=0.191 - 0.81 = 0.19

Therefore, the probability that at least one of the two students is not carrying an umbrella is 19%.

The correct answer is 19%.

Would you like further explanation on this?

Here are 5 related questions you could consider:

  1. What is the probability that both students are not carrying umbrellas?
  2. How does the probability change if three students walk into the classroom?
  3. What if 80% of the students were carrying umbrellas instead of 90%? How would the probability change?
  4. How would the calculation differ if we wanted the probability of exactly one student not carrying an umbrella?
  5. How would this scenario change if there were dependent events rather than independent events?

Tip: In problems involving "at least one" scenarios, it's often easier to calculate the complement event (in this case, both students carrying umbrellas) and subtract it from 1.

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Math Problem Analysis

Mathematical Concepts

Probability
Complementary Events

Formulas

Probability that a student is not carrying an umbrella = 1 - 0.9
Probability that both students are carrying umbrellas = 0.9 * 0.9
Probability that at least one is not carrying an umbrella = 1 - Probability that both are carrying umbrellas

Theorems

Law of Complements

Suitable Grade Level

Grades 10-12