Question

A standard reference material is certified to contain 93.5 ppm of an organic contaminant in water. A student's analysis gives values of 98.6, 98.4, 97.5, 94.3, and 97.0 ppm. Do the students results differ from the expected value at the 95% confidence level?

Answer 1

H0: = 93.5

Ha: 93.5

From sample data, = 97.16 , S = 1.72714

Test statistics

t = - / S / sqrt(n)

= 97.16 - 93.5 / 1.72714 / sqrt(5)

= 4.74

t critical value at 0.05 level with 4 df = -2.776 , 2.776

Since test statistics falls in rejection region, we have sufficient evidence to reject H0.

We conclude at 0.05 level that students results differ from the expected value,