Math Problem Statement

Assume the random variable X is normally distributed with mean μ = 50 and standard deviation σ = 7. Find the probability P(X > 35).

Solution

To solve the problem, we need to calculate the probability P(X>35)P(X > 35), where XX is a normally distributed variable with a mean μ=50\mu = 50 and a standard deviation σ=7\sigma = 7.

Step 1: Standardize the Variable

We convert X=35X = 35 into a standard normal variable ZZ using the formula: Z=XμσZ = \frac{X - \mu}{\sigma} Substituting the values: Z=35507=1572.14Z = \frac{35 - 50}{7} = \frac{-15}{7} \approx -2.14

Step 2: Find P(Z>2.14)P(Z > -2.14)

Using the symmetry of the standard normal distribution: P(Z>2.14)=1P(Z2.14)P(Z > -2.14) = 1 - P(Z \leq -2.14)

From standard normal tables or a calculator, the cumulative probability P(Z2.14)P(Z \leq -2.14) is approximately 0.0162.

Thus: P(Z>2.14)=10.0162=0.9838P(Z > -2.14) = 1 - 0.0162 = 0.9838

Step 3: Interpret the Result

The probability P(X>35)P(X > 35) is approximately 0.9838.

Would you like a detailed breakdown or graph of the normal distribution for better understanding?

Here are five related questions for practice:

  1. What is P(X<45)P(X < 45) for the same distribution?
  2. How do you calculate P(40<X<60)P(40 < X < 60) for a normal distribution?
  3. What is the probability P(X>60)P(X > 60)?
  4. How do you interpret P(X>μ)P(X > \mu) for any normal distribution?
  5. How do you find probabilities for non-standard normal distributions?

Tip: Always standardize the random variable when working with normal distributions to make use of standard normal tables or calculators!

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Math Problem Analysis

Mathematical Concepts

Normal distribution
Standardization
Probability

Formulas

Z = (X - μ) / σ
P(Z > z) = 1 - P(Z ≤ z)

Theorems

Standard normal distribution properties

Suitable Grade Level

College/University level (Introductory Statistics)