The following table gives the average high temperatures in January and July for several European Cities. Write a 90% confidence interval for the mean temperature difference summer and winter in Europe. Be sure to check conditions for inference, and clearly explain what your interval means.
City ------------Jan.----July
Vienna---------34------75
Copenhagan--36-----72
Paris------------42-----76
Berlin-----------35------74
Athens----------54-----90
Rome------------54-----88
Amsterdam----40------69
Madrid-----------47------87
London----------44-------73
Edinburgh------43------65
Moscow--------21-------76
Belgrade-------37--------84