Answer with explanation:
Let
be the population mean .
By considering the given information in the question , we have

Here,
is two-tailed , so the test is a two-tailed test.
Also, population standard deviation is unknown , so we perform a two-tailed t-test.
For sample size : n= 18
Sample mean :

Sample standard deviation : s=0.80
Test statistic :





Two-tailed Critical values for
and degree of freedom df=n-1=17

Decision : Since the calculated t-value(2.39) does not lie between the critical values -2.11 and 2.11.
So we reject the null hypothesis .
Conclusion : We have enough evidence at 0.05 significance level to support the claim that the sample estimate is different from the company’s expected weight of 20 oz.