English teacher has been teaching a sixth grade composition class for many years.He has the feeling that over the past several years,the writing ability of students has changed.A national test of proficiency in composition wasadministered5yearsago.The resulting distribution of scores was normally shaped,had a mean of80and a standard deviation of11.In order to test his feeling,he gives his present class of40students the same proficiency test.The resulting mean is70and the standard deviation is8.

1.CalculatetheobtainedstatisticusingZ test

2. Find thecritvalue using Z test, two tailed, alpha = 0.01

3. Report your conclusion