Răspuns :
(12 + 24 + 36 + ....+ 144) : ( 1 + 2 + 3 + .. + 12) =
12 x ( 1 + 2 + ... + 12) : ( 1 + 2+ ...+ 12) = 12
12 x ( 1 + 2 + ... + 12) : ( 1 + 2+ ...+ 12) = 12