[bpizzi]

For the posterity: {a+b=10;a-b=1} translates to {a+b=10;a=b +1}, thus the first equation is ((b+1)+b=10) giving (b=4.5), and from there we get (a=5.5).

[LolWolf]

Another fun way: add the two equations to get 2A=11 and subtract to get 2B=9.