To find the mean time for Group A:
(18 + 20 + 46 + 34 + 58 + 31 + 41) / 7 = 37.4 minutes
To find the mean time for Group B:
(15 + 21 + 32 + 42 + 29 + 57 + 39) / 7 = 33.4 minutes
The mean time Group A spent shopping is 37.4 minutes.
The mean time Group B spent shopping is 33.4 minutes.
The mean times Group A and Group B spent shopping differ by 4.0 minutes.