Question

Repeat analyses of the sulphate in ground waters using a gravimetric analysis technique yielded the following data for successive samples: 27.4, 27.6, 25.2, 27.3, 27.3 ppm sulphate. Using 95% confidence criteria which of the following statements is true?

Select one:

a. 25.2 should be rejected

b. 27.4 should be rejected

c. 25.2 and 27.4 should be rejected

d. no data should be rejected

Answer 1

Correct option:

a. 25.2 should be rejected

Explanation:

From the given data, the following Table is calculated:

n = 5

x	(x - )	(x - )2
27.4	0.44	0.1936
27.6	0.64	0.4096
25.2	- 1.76	3.0976
27.3	0.34	0.1156
27.3	0.34	0.1156
Total =		3.9320

SE = s/

= 0.9915/

= 0.4434

= 0.05

ndf = n - 1 = 5 - 1 = 4

From Table, critical values of t = 2.7764

Confidence Interval:

26.96 (2.7764 X 0.4434)

= 26.96 1.2311

= (25.7289 ,28.1911)

Since 25.2 is not included in the Confidence Interval, 25.2 should be rejected.

Since 27.4 is included in the Confidence Interval, 25.2 should not be rejected.

So,

Correct option:

a. 25.2 should be rejected