Answer:
Step-by-step explanation:
Mean = (11.4 + 13.9 + 11.2 + 14.5 + 15.2 + 8.1 + 12.4 + 8.6 + 10.5 + 17.1 + 9.8 + 15.9)/12 = 12.4
Standard deviation = √(summation(x - mean)²/n
n = 12
Summation(x - mean)² = (11.4 - 12.4)^2 + (13.9 - 12.4)^2 + (11.2 - 12.4)^2+ (14.5 - 12.4)^2 + (15.2 - 12.4)^2 + (8.1 - 12.4)^2 + (12.4 - 12.4)^2 + (8.6 - 12.4)^2 + (10.5 - 12.4)^2 + (17.1 - 12.4)^2 + (9.8 - 12.4)^2 + (15.1 - 12.4)^2 = 89.62
Standard deviation = √(89.62/13) = 2.7
We would set up the hypothesis test. This is a test of a single population mean since we are dealing with mean
a) For the null hypothesis,
µ ≤ 15
For the alternative hypothesis,
µ > 15
This is a right tailed test
b) Since the number of samples is small and no population standard deviation is given, the distribution is a student's t.
Since n = 12,
Degrees of freedom, df = n - 1 = 12 - 1 = 11
t = (x - µ)/(s/√n)
Where
x = sample mean = 12.4
µ = population mean = 15
s = samples standard deviation = 2.7
t = (12.4 - 15)/(2.7/√12) = - 3.34
We would determine the p value using the t test calculator. It becomes
p = 0.0034
c) Assuming level of significance = 0.05.
Since alpha, 0.05 > than the p value, 0.0034, then we would reject the null hypothesis. Therefore, At a 5% level of significance, we can conclude that the water from this source does meets the EPA standard. They are higher than 15ppb
