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Concentration of SO2 ( in ppm) | Frequency |
0.00 – 0.04 | 4 |
0.04 – 0.08 | 9 |
0.08 – 0.12 | 9 |
0.12 – 0.16 | 2 |
0.16 – 0.20 | 4 |
0.20 – 0.24 | 2 |
Answer :
Calculate mean by direct method:
Concentration of SO2 (in ppm) | Frequency \( ( f_i ) \) | Mid-point \( (x_i) \) | \( f_i x_i \) |
0.00 - 0.04 | 4 | 0.02 | 0.08 |
0.04 - 0.08 | 9 | 0.06 | 0.54 |
0.08 - 0.12 | 9 | 0.10 | 0.90 |
0.12 - 0.16 | 2 | 0.14 | 0.28 |
0.16 - 0.20 | 4 | 0.18 | 0.72 |
0.20 - 0.24 | 2 | 0.20 | 0.40 |
Total | \( \sum f_i \ = \ 30 \) | \( \sum f_i x_i \ = \ 2.96 \) |
The formula to find out the mean is
\( \overline{x} \ = \ \frac{ \sum \ f_i x_i}{ \sum f_i} \)
\( = \ \frac{2.96}{30} \)
\( = \ 0.099 \) ppm
\(\therefore \) The mean concentration of SO2 in air is 0.099 ppm.