Answer:
The null hypothesis is [tex]H_0: \mu = X[/tex]
The alternate hypothesis is [tex]H_1: \mu \neq X[/tex]
Step-by-step explanation:
Mean of X in 1990, test if the mean duration has changed:
At the null hypothesis, we test if the mean duration is still X, that is:
[tex]H_0: \mu = X[/tex]
At the alternate hypothesis, we test if the mean duration has the changed, that is, if it is different of X. So
[tex]H_1: \mu \neq X[/tex]