Question

$(2 + 4 + 6 + ... + 20) - (1 + 3 + 5 + ... + 19)$

Answer 1

(2+4+6+....+20)-(1+3+5+...+19)=

(2-1)+(4-3)+...+(20-19)=

1+1+1+...+1=10

de 10 ori