Question

Strength of concrete: The compressive strength, in kilopascals, was measured for concrete blocks from five different batches of concrete, both three and six after pouring. The data are as follows. Can you conclude that the mean strength after three days is less than the mean strength after six days? Let U1 represent the mean strength after three days and ud=u1-u2, Use the a=0.01 level and the critical value method with the table.

1. State the appropriate null and alternate hypotheses.

2. Test Statistics

3. Degrees of Freedom using the simple method?

4. What is the critical value?

5. Determine whether to reject H0.

6. State a conclusion.

Block	After 3 days	After 6 days
1	1362	1364
2	1350	1390
3	1366	1377
4	1341	1361
5	1372	1370

Answer 1

1)

null Hypothesis:		μd	=	0
alternate Hypothesis:		μd	<	0

2)

test statistic            =

(d̅-μd)/Se         =

-1.897

3)

degree of freedom =n-1                            =

4.000

4)

critical value t =-3.747

5)fail to reject Ho

6) we can not conclude that t the mean strength after three days is less than the mean strength after six days