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AI Fusion Summary
Let’s break down the problem step by step.
We are given:
- The total number of students: \( n = 100 \)
- The mean score: \( \bar{x} = 40 \)
- The standard deviation: \( s = 10 \)
We are asked to find the number of students who scored between 30 and 50.
---
### Step 1: Standardize the scores
We convert the scores to z-scores using the formula:
\[
z = \frac{x - \bar{x}}{s}
\]
For \( x = 30 \):
\[
z_{30} = \frac{30 - 40}{10} = \frac{-10}{10} = -1
\]
For \( x = 50 \):
\[
z_{50} = \frac{50 - 40}{10} = \frac{10}{10} = 1
\]
So, we are looking for the proportion of students with z-scores between -1 and 1.
---
### Step 2: Use the empirical rule
The empirical rule (68-95-99.7 rule) states that approximately 68% of the data lies within one standard deviation of the mean in a normal distribution.
So, the proportion of students scoring between 30 and 50 is approximately 68%.
---
### Step 3: Calculate the number of students
\[
\text{Number of students} = 0.68 \times 100 = 68
\]
---
### Step 4: Check the options
The options given are:
- A) 68
- B) 95
- C) 99
- D) 100
So, the answer should be **A) 68**.
---
**Final answer:**
\[
\boxed{A}
\]
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