a. The standard error is equal to the standard deviation divided by the square root of the sample size:
SE = (23 ppm)/√18 ≈ 5.42 ppm
b. The t statistic is given by the difference between the true and sample means, divided by the standard error:
t = (192 ppm - 180 ppm)/SE ≈ 2.21
c. The p-value is approximately 0.0204.
d. Since p < 0.05, the difference is significantly different, so we reject the null hypothesis.
e. A type I error might have occurred, since it's possible that the null hypothesis was true, but we ended up rejecting it.