Question

Calculati:
S=3+6+9+...+255
S=2+4+6...80​

Answer 1

S=3+6+9+...+255

S=3(1+2+3+...+85)

S=3*[85*(85+1)]/2

S=3*(85*86)/2

S=3*85*43

S=10945

S=2+4+6+...+80

S=2(1+2+3+...+40)

S=2*[40*(40+1)]/2

S=40*41

S=1640