Finding a Value in a Normal Distribution

MathematicsStatistics - Normal DistributionMedium

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Given the normal distribution with $\mu = 200$ and $\sigma = 10$, the $x$ value that has $35\%$ of the area above it is ________. (Round off your answer to the nearest tenths)

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1
Step 1

In this problem, we are given a normal distribution and asked to find a specific x value based on the area above it.

Normal Distribution Problem

2
Step 2

Let's list the known parameters: the mean mu is two hundred, and the standard deviation sigma is ten.

$$\mu = 200, \sigma = 10$$
3
Step 3

We are looking for an x value such that thirty-five percent of the area is above it. This means the area to the right of x is zero point three five.

$$P(X > x) = 0.35$$
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Step 4

Since standard normal distribution tables usually show the area to the left, we calculate that as one minus zero point three five, which equals zero point six five.

$$P(X < x) = 1 - 0.35 = 0.65$$
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Step 5

Let's visualize this on a normal distribution curve.

Visualizing the Area

35% Above65% Belowx = ?
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Step 6

Now we need to find the z-score that corresponds to a cumulative area of zero point six five. Using a standard normal table or calculator, we find z is approximately zero point three eight five.

$$z_{0.65} \approx 0.385$$

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About This Question

Subject
Mathematics
Topic
Statistics - Normal Distribution
Difficulty
Medium
Question Type
Open Ended

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