Math Problem Statement

n a process for manufacturing glassware, glass stems are sealed by heating them in a flame. The temperature of the flame varies a bit. The following table is the distribution of the temperature X measure in degrees Celsius: Temperature 540 545 550 555 560 Probability 0.1 0.1 0.3 0.25 0.25 What is the standard deviation σX? (Round answer to the nearest thousandth.)

Solution

To calculate the standard deviation σX\sigma_X of the temperature distribution, we'll use the formula for standard deviation in a discrete probability distribution:

σX=(xiμ)2P(xi)\sigma_X = \sqrt{\sum (x_i - \mu)^2 \cdot P(x_i)}

Where:

  • xix_i are the temperature values
  • P(xi)P(x_i) are the corresponding probabilities
  • μ\mu is the mean (expected value) of the distribution

Step 1: Calculate the Mean μ\mu

The mean μ\mu for a discrete probability distribution is calculated as:

μ=xiP(xi)\mu = \sum x_i \cdot P(x_i)

Using the given dataTo calculate the standard deviation σX\sigma_X of the temperature distribution, we'll use the formula for standard deviation in a discrete probability distribution:

σX=(xiμ)2P(xi)\sigma_X = \sqrt{\sum (x_i - \mu)^2 \cdot P(x_i)}

Where:

  • xix_i are the temperature values
  • P(xi)P(x_i) are the corresponding probabilities
  • μ\mu is the mean (expected value) of the distribution

Step 1: Calculate the Mean μ\mu

The mean μ\mu for a discrete probability distribution is calculated as:

μ=xiP(xi)\mu = \sum x_i \cdot P(x_i)

Using the given

μ=(5400.1)+(5450.1)+(5500.3)+(5550.25)+(5600.25)\mu = (540 \cdot 0.1) + (545 \cdot 0.1) + (550 \cdot 0.3) + (555 \cdot 0.25) + (560 \cdot 0.25)

μ=54+54.5+165+138.75+140=552.25\mu = 54 + 54.5 + 165 + 138.75 + 140 = 552.25

So, the mean μ\mu is 552.25°C.

Step 2: Calculate the Variance

The variance is:

σX2=(xiμ)2P(xi)\sigma_X^2 = \sum (x_i - \mu)^2 \cdot P(x_i)

Now we'll calculate each term in this sum:

  1. For x1=540x_1 = 540: (540552.25)2=(12.25)2=150.0625(540 - 552.25)^2 = (-12.25)^2 = 150.0625 Contribution to variance: 150.06250.1=15.00625150.0625 \cdot 0.1 = 15.00625

  2. For x2=545x_2 = 545: (545552.25)2=(7.25)2=52.5625(545 - 552.25)^2 = (-7.25)^2 = 52.5625 Contribution to variance: 52.56250.1=5.2562552.5625 \cdot 0.1 = 5.25625

  3. For x3=550x_3 = 550: (550552.25)2=(2.25)2=5.0625(550 - 552.25)^2 = (-2.25)^2 = 5.0625 Contribution to variance: 5.06250.3=1.518755.0625 \cdot 0.3 = 1.51875

  4. For x4=555x_4 = 555: (555552.25)2=2.752=7.5625(555 - 552.25)^2 = 2.75^2 = 7.5625 Contribution to variance: 7.56250.25=1.8906257.5625 \cdot 0.25 = 1.890625

  5. For x5=560x_5 = 560: (560552.25)2=7.752=60.0625(560 - 552.25)^2 = 7.75^2 = 60.0625 Contribution to variance: 60.06250.25=15.01562560.0625 \cdot 0.25 = 15.015625

Now, sum these contributions:

σX2=15.00625+5.25625+1.51875+1.890625+15.015625=38.6875\sigma_X^2 = 15.00625 + 5.25625 + 1.51875 + 1.890625 + 15.015625 = 38.6875

Step 3: Calculate the Standard Deviation

Finally, take the square root of the variance:

σX=38.6875=6.220\sigma_X = \sqrt{38.6875} = 6.220

So, the standard deviation σX\sigma_X is 6.220°C (rounded to the nearest thousandth).


Would you like further clarification on any part of this solution?

Here are some related questions you might find helpful:

  1. How is the mean calculated for discrete probability distributions?
  2. What is the significance of variance in a data set?
  3. Can standard deviation be negative?
  4. How does the shape of the distribution relate to standard deviation?
  5. What are other ways to measure spread in a data set?

Tip: When interpreting standard deviation, a smaller value indicates that the data points are closer to the mean, while a larger value indicates more spread.

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Math Problem Analysis

Mathematical Concepts

Statistics
Discrete Probability Distribution
Standard Deviation

Formulas

Standard deviation formula for discrete probability distributions: σX = sqrt(Σ(xi - μ)^2 * P(xi))
Mean formula for discrete probability distributions: μ = Σxi * P(xi)

Theorems

Properties of Standard Deviation in Probability Distributions

Suitable Grade Level

Grades 11-12