I can't understand how decimal designation differ by power of 2??

 

Of A = 1 and B = 1 then A B = 11. In decimal notation that is 3.

When you group with other terms only one of the inputs A or B can change. So, the only options of a group with 11 are 01 or 10, since 00 changes more than one term. Binary 11 is decimal 3. Binary 01 is decimal 1, a change by 2 or 2^1. Binary 10 is 2, a change is 1 or 2^0.

Binary 00 is decimal 0, a change of 3, not a power of 2.