Question

use doubles minus one to solve 8´+7

Answer 1

Well we have
8 + 7. The method used would be like thos
8 + 7 
~2(-1) + 10 + 7
~-2 + 10 + 7
~8 + 7
Double minus one is this here > (-1) + (-1) = -1 - 1 = -2 = 2(-1)