Math Problem Statement

5. A measurement x in a sample with mean 2.3 and standard deviation 1.3 has a z-score equal to -2.

What is x?

[A] -0.3 [B] 4.6 [C] 4.9 [D] -2.6

Solution

To solve for the value of x given that the z-score is -2, the mean is 2.3, and the standard deviation is 1.3, we can use the formula for the z-score:

z=xμσz = \frac{x - \mu}{\sigma}

Where:

  • zz is the z-score,
  • μ\mu is the mean,
  • σ\sigma is the standard deviation, and
  • xx is the value we're solving for.

Plugging in the known values:

2=x2.31.3-2 = \frac{x - 2.3}{1.3}

Now, solve for xx:

  1. Multiply both sides by 1.3: 2×1.3=x2.3-2 \times 1.3 = x - 2.3 2.6=x2.3-2.6 = x - 2.3

  2. Add 2.3 to both sides: x=2.6+2.3x = -2.6 + 2.3 x=0.3x = -0.3

Thus, the value of x is 0.3-0.3, which corresponds to option [A] -0.3.

Would you like more details on z-scores or any further explanations?


Here are 5 related questions to explore this topic further:

  1. How would the z-score change if x was greater than the mean?
  2. What does a z-score of 0 represent in a dataset?
  3. How do you interpret positive and negative z-scores in terms of standard deviations?
  4. How can z-scores be used to compare measurements from different datasets?
  5. What is the relationship between the standard deviation and the spread of data?

Tip: A z-score represents how many standard deviations a data point is from the mean. A negative z-score indicates the point is below the mean.

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Math Problem Analysis

Mathematical Concepts

Statistics
Z-score
Standard Deviation
Mean

Formulas

z = (x - μ) / σ

Theorems

-

Suitable Grade Level

Grades 9-12