First, don't write equations with percents- percents are not numbers and that is what is causing your confusion. Every percent requires knowing what base you are talking about. The first "A is larger than B by 10%" means that A is larger than B by 10%of B: A= B(1+ 0.10)= 1.1B. "B is smaller than A by 10%" means that B is less than A by 10%of A.

For example, if B= 100 and A= 110 then "A is 10% bigger than B": 10% of 100 is 10 and 100+ 10= 110. But 10% of A is 11 and 110- 11= 99, not 100. B isnot"10% less than A".

By the way, your English is excellent. Far better than my ________ (put any language you like here!).