Answer:

Step-by-step explanation:
From the given information:
The sample size is 28
The population mean is 24.5 (ppb)
The sample mean is 225.3 (ppb)
Thus, the null and the alternative hypothesis can be computed as:
Null hypothesis:

Alternative hypothesis:

Answer:
p value = 0.039
t = - 2.169
Step-by-step explanation:
Applying the null and alternate hypothesis

using excel worksheet to calculate for ( t and p )
t = -2.169
p = 0.039
from the results obtained
The conclusion is affected by the significance level because : 0.1 < p > 0.01
so when the significance level is = 0.1 the Null hypothesis is rejected and we can say the mean time interval will change while
if the significance level = 0.01 the Null hypothesis is accepted and we can not say the mean time interval has changed because the p -value is greater than 0.01
attached is the excel solution