The mean of the observation 7, 8, 9, 11 and 15 is 10.

Answer

To find the mean of the observations 7, 8, 9, 11, and 15, we will follow these steps:

### Step 1: List the Observations
The given observations are:
- 7
- 8
- 9
- 11
- 15

### Step 2: Calculate the Sum of the Observations
We need to add all the observations together:
\[ 7 + 8 + 9 + 11 + 15 \]

Calculating step-by-step:
- First, add 7 and 8:
\[ 7 + 8 = 15 \]
- Next, add the result to 9:
\[ 15 + 9 = 24 \]
- Then, add 11:
\[ 24 + 11 = 35 \]
- Finally, add 15:
\[ 35 + 15 = 50 \]

So, the sum of the observations is \( 50 \).

### Step 3: Count the Number of Observations
Now, we count how many observations we have:
- The observations are 7, 8, 9, 11, and 15.
- There are a total of 5 observations.

### Step 4: Calculate the Mean
To find the mean, we divide the sum of the observations by the number of observations:
\[ \text{Mean} = \frac{\text{Sum of Observations}}{\text{Number of Observations}} = \frac{50}{5} \]

Calculating this gives:
\[ \text{Mean} = 10 \]

### Final Answer
The mean of the observations 7, 8, 9, 11, and 15 is \( 10 \).

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