# Environmental Science: Numerical Questions – Statistics Sd and Sem

Dr. Manishika Jain- Join online Paper 1 intensive course. Includes tests and expected questions.

## Type I – Standard Deviation

1. In a city, the daily per capita inhalation (m^{3}) values of contaminated air over a period of 5 days are 6.3,6.3,6.2,6.4 and 5.8, respectively. The sample mean with standard deviation of the data is

- 6.2 ± 0.02
- 6.2 ± 0.23
- 6.0 ± 0.15
- 6.2 ± 0.18

Answer: (B) 6.2 ± 0.23

Explanation: Mean =

=

=

= = 6.2

Standard Deviation =

6.3 | 6.3 - 6.2 = 0.1 | 0.01 |

6.3 | 6.3 - 6.2 = 0.1 | 0.01 |

6.2 | 6.2 - 6.2 = 0 | 0 |

6.4 | 6.4 - 6.2 = 0.2 | 0.04 |

5.8 | 5.8 - 6.2 =-0.4 | 0.16 |

Σ 0.22 |

## Type II – Standard Error of Mean

2. In random samples of 64 boats out of a total 2400 boats, the mean number of defective boats is 3.2 with a sample standard deviation 0.8. The standard error of the mean is

- ~0.107
- ~0.40
- ~0.97
- ~0.097

Answer: (D) ~0.97

Explanation: Standard Error of Mean (SEM) =

=

= 0.8/8

= 0.1

## Type III – Sample Size

3. If the standard deviation of a population is 20 and the standard error of mean is 4, then the sample size is:

- 25
- 80
- 5
- 100

Answer: (A) 25

Explanation: Standard Error of Mean (SEM) =

4 =

= 20/4 = 5

S0, n = (5) ^{2} = 25

-Mayank