Question

[900-(1+2+3...+40)] ×80-80×80=​

Answer 1

1+2+3+...+40=40*41/2=820

Deci (900-820)*80-80*80 = 80*(900-820-80) =80*0=0 (L-am dat pe 80 factor comun)

Answer 2

[900-(1+2+3+...+40)]x 80-80x80=

[900-(40x41:2)]x80-720

[900-(1640:2)]x80-720

(900-820)x80-720

80x80-720

720-720=0