Questions: Assume that adults have IQ scores that are normally distributed with a mean of μ=105 and a standard deviation σ=15. Find the probability that a randomly selected adult has an IQ less than 126. The probability that a randomly selected adult has an IQ less than 126 is (Type an integer or decimal rounded to four decimal places as needed.)

Assume that adults have IQ scores that are normally distributed with a mean of μ=105 and a standard deviation σ=15. Find the probability that a randomly selected adult has an IQ less than 126.

The probability that a randomly selected adult has an IQ less than 126 is 
(Type an integer or decimal rounded to four decimal places as needed.)
Transcript text: Assume that adults have IQ scores that are normally distributed with a mean of $\mu=105$ and a standard deviation $\sigma=15$. Find the probability that a randomly selected adult has an IQ less than 126. Click to view page 1 of the table. Click to view page 2 of the table. The probability that a randomly selected adult has an IQ less than 126 is $\square$ (Type an integer or decimal rounded to four decimal places as needed.)
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Solution

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Solution Steps

Step 1: Define the Normal Distribution Parameters

We are given that the IQ scores of adults are normally distributed with a mean μ=105 \mu = 105 and a standard deviation σ=15 \sigma = 15 .

Step 2: Calculate the Z-Score

To find the probability that a randomly selected adult has an IQ less than 126, we first calculate the Z-score for X=126 X = 126 using the formula:

Z=Xμσ Z = \frac{X - \mu}{\sigma}

Substituting the values:

Zend=12610515=2115=1.4 Z_{end} = \frac{126 - 105}{15} = \frac{21}{15} = 1.4

Step 3: Determine the Probability

The probability that a randomly selected adult has an IQ less than 126 can be expressed as:

P(X<126)=Φ(Zend)Φ(Zstart) P(X < 126) = \Phi(Z_{end}) - \Phi(Z_{start})

Where Zstart Z_{start} approaches negative infinity. Thus, we have:

P(X<126)=Φ(1.4)Φ()=Φ(1.4) P(X < 126) = \Phi(1.4) - \Phi(-\infty) = \Phi(1.4)

Using the standard normal distribution table or a calculator, we find:

Φ(1.4)0.9192 \Phi(1.4) \approx 0.9192

Final Answer

The probability that a randomly selected adult has an IQ less than 126 is:

0.9192 \boxed{0.9192}

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