A Manufacturer of Cordless Electric Shavers Sampled 13 from a Day's

A manufacturer of cordless electric shavers sampled 13 from a day's production
And found the mean time of continuous usage without recharging to be 410 minutes with a sample standard deviation of 30 minutes. We can assume that times are normally
Distributed. We wish to test if the true mean operating time without recharging is more
Than 400 minutes. The correct null and alternative hypotheses are A. $\quad \mathrm { H } _ { 0 } : \mu = 400 ; \mathrm { H } _ { \mathrm { A } } : \mu < 400$
B. $\mathrm { H } _ { 0 } : \mu = 400 ; \mathrm { H } _ { \mathrm { A } } : \mu > 400$
C. $\mathrm { H } _ { 0 } : \mu > 400 ; \mathrm { H } _ { \mathrm { A } } : \mu = 400$
D. $\mathrm { H } _ { 0 } : \mu < 400 ; \mathrm { H } _ { \mathrm { A } } : \mu = 400$
E. $\mathrm { H } _ { 0 } : \mu = 400 ; \mathrm { H } _ { \mathrm { A } } : \mu \neq 400$