Question 168 of 480
Find the variance of 2, 6, 8, 6, 2 and 6
Correct Answer:
B
Explanation
To find the variance of the given set of numbers (2, 6, 8, 6, 2, and 6), we will follow a systematic approach. Let's break it down step-by-step.
### Step 1: Calculate the Mean
The first step in finding the variance is to calculate the mean (average) of the data set.
**Formula for Mean:**
\[
\text{Mean} (\mu) = \frac{\text{Sum of all data points}}{\text{Number of data points}}
\]
**Calculating the Mean:**
- Sum of the data points: \(2 + 6 + 8 + 6 + 2 + 6 = 30\)
- Number of data points: \(6\)
Now, we can calculate the mean:
\[
\mu = \frac{30}{6} = 5
\]
### Step 2: Calculate the Variance
Variance measures how far each number in the set is from the mean and thus from every other number in the set.
**Formula for Variance:**
\[
\text{Variance} (\sigma^2) = \frac{\sum (x_i - \mu)^2}{N}
\]
where \(x_i\) represents each data point, \(\mu\) is the mean, and \(N\) is the number of data points.
**Calculating Each Squared Deviation:**
Now, we will calculate the squared deviation of each data point from the mean:
1. For \(x_1 = 2\):
\[
(2 - 5)^2 = (-3)^2 = 9
\]
2. For \(x_2 = 6\):
\[
(6 - 5)^2 = (1)^2 = 1
\]
3. For \(x_3 = 8\):
\[
(8 - 5)^2 = (3)^2 = 9
\]
4. For \(x_4 = 6\):
\[
(6 - 5)^2 = (1)^2 = 1
\]
5. For \(x_5 = 2\):
\[
(2 - 5)^2 = (-3)^2 = 9
\]
6. For \(x_6 = 6\):
\[
(6 - 5)^2 = (1)^2 = 1
\]
### Step 3: Sum of Squared Deviations
Now, we sum all the squared deviations:
\[
9 + 1 + 9 + 1 + 9 + 1 = 30
\]
### Step 4: Calculate the Variance
Now we can calculate the variance using the sum of squared deviations:
\[
\sigma^2 = \frac{30}{6} = 5
\]
### Conclusion
The variance of the data set (2, 6, 8, 6, 2, 6) is **5**.
### Explanation of Options
- **Option A (6)**: This is incorrect because it does not match our calculated variance of 5.
- **Option B (5)**: This is the correct answer as we calculated the variance to be 5.
- **Option C (√6)**: This is incorrect because it represents the square root of a number, not the variance itself.
- **Option D (√5)**: This is also incorrect as it represents the square root of the variance, not the variance itself.
### Revision Summary
- The variance is calculated by finding the mean, then determining the squared deviations from the mean, summing those, and dividing by the number of data points.
- The mean of the data set (2, 6, 8, 6, 2, 6) is 5.
- The variance of the data set is 5.
- Always ensure to differentiate between variance and its square root (standard deviation).