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To find out the concentration of [tex]SO_2[/tex] in the air (in parts per million, i.e., ppm), data was collected for 30 localities in a certain city and is presented below:

\begin{tabular}{|l|c|c|c|c|c|c|}
\hline
Concentration of [tex]SO_2[/tex] in ppm & 0.00-0.04 & 0.04-0.08 & 0.08-0.12 & 0.12-0.16 & 0.16-0.20 & 0.20-0.24 \\
\hline
Frequency & 4 & 9 & 9 & 2 & 4 & 2 \\
\hline
\end{tabular}

Find the mean concentration of [tex]SO_2[/tex] in the air.


Sagot :

To calculate the mean concentration of [tex]\( SO_2 \)[/tex] in the air, we'll follow these steps:

### Step 1: Identify the Concentration Ranges and Frequencies
We have the concentration ranges and their corresponding frequencies provided in the data:
[tex]\[ \begin{array}{|c|c|c|c|c|c|c|} \hline \text{Concentration range (ppm)} & 0.00-0.04 & 0.04-0.08 & 0.08-0.12 & 0.12-0.16 & 0.16-0.20 & 0.20-0.24 \\ \hline \text{Frequency} & 4 & 9 & 9 & 2 & 4 & 2 \\ \hline \end{array} \][/tex]

### Step 2: Calculate Midpoints of Each Concentration Range
To find the midpoint for each range, we use the formula for the midpoint [tex]\[ \text{Midpoint} = \frac{\text{Lower Boundary} + \text{Upper Boundary}}{2} \][/tex]

- For the range [tex]\( 0.00-0.04 \)[/tex]: [tex]\(\text{Midpoint} = \frac{0.00 + 0.04}{2} = 0.02\)[/tex]
- For the range [tex]\( 0.04-0.08 \)[/tex]: [tex]\(\text{Midpoint} = \frac{0.04 + 0.08}{2} = 0.06\)[/tex]
- For the range [tex]\( 0.08-0.12 \)[/tex]: [tex]\(\text{Midpoint} = \frac{0.08 + 0.12}{2} = 0.10\)[/tex]
- For the range [tex]\( 0.12-0.16 \)[/tex]: [tex]\(\text{Midpoint} = \frac{0.12 + 0.16}{2} = 0.14\)[/tex]
- For the range [tex]\( 0.16-0.20 \)[/tex]: [tex]\(\text{Midpoint} = \frac{0.16 + 0.20}{2} = 0.18\)[/tex]
- For the range [tex]\( 0.20-0.24 \)[/tex]: [tex]\(\text{Midpoint} = \frac{0.20 + 0.24}{2} = 0.22\)[/tex]

Thus, the midpoints are:
[tex]\[ [0.02, 0.06, 0.10, 0.14, 0.18, 0.22] \][/tex]

### Step 3: Apply Frequency to Each Midpoint
Now, multiply each midpoint by its corresponding frequency to get the weighted values:

- [tex]\(0.02 \times 4 = 0.08\)[/tex]
- [tex]\(0.06 \times 9 = 0.54\)[/tex]
- [tex]\(0.10 \times 9 = 0.90\)[/tex]
- [tex]\(0.14 \times 2 = 0.28\)[/tex]
- [tex]\(0.18 \times 4 = 0.72\)[/tex]
- [tex]\(0.22 \times 2 = 0.44\)[/tex]

### Step 4: Sum Up the Frequencies and the Weighted Values
Sum of the frequencies:
[tex]\[ 4 + 9 + 9 + 2 + 4 + 2 = 30 \][/tex]

Sum of the weighted values:
[tex]\[ 0.08 + 0.54 + 0.90 + 0.28 + 0.72 + 0.44 = 2.96 \][/tex]

### Step 5: Calculate the Mean Concentration
The mean concentration is calculated by dividing the total of the weighted values by the sum of the frequencies:
[tex]\[ \text{Mean Concentration} = \frac{\text{Total Weighted Value}}{\text{Total Frequency}} = \frac{2.96}{30} = 0.0987 \][/tex]

Thus, the mean concentration of [tex]\( SO_2 \)[/tex] in the air is approximately:
[tex]\[ 0.0987 \text{ ppm} \][/tex]