A new energy drink is supposed to improve a person’s time in the one mile run. The times, in seconds, of eight runners with and without the drink are given below:

Runner                 1      2      3    4    5    6    7   8

x-time (before)    254 276 276  265 271  273  268 281

y-time (after)       265 269 277  279 266  273  275 279

Find the 95 % confidence interval for mean of the differences, µd.