**9. Correct. The answer is true**

The test can be formulated has follow:

H_{0}: μ_{ }= 0.25_{}

H_{1:} μ_{ }≠ 0.25_{}

T = ((`x_{ }- μ )*(n-1)^{0.5})/s

T = (0.28-0.25)*9^{0.5}/0.003

T= 3

a) At 5%

Tcalulated > T table => We reject the null hypothesis
at 5% level of significance.

b) At 1%

Tcalculated < T table => We fail to reject the
null hypothesis at 1% level of significance**.**