What is the total no of ways of selecting atleast one item from each of the two sets containing 6 different items each?

We can select atleast one item from 6 different items =  $26-1$  

Similarly we can select atleast one item from other set of 6 different items in  $26-1$ ways. 

Required number of ways =  $(26-1)26-1 = 26-12$ = 3969