A/4 + B/4 + C/4 + D/4 + E = 90; B/4 + C/4 + D/4 + E/4 + A = 105; A/4 + C/4 + D/4 + E/4 + B = 110; A/4 + B/4 + D/4 + E/4 + C = 125; A/4 + B/4 + C/4 + E/4 + D = 150; 5式相加: A + B + C + D + E + E + A + B + C + D = 580 A + B + C + D + E = 580/2= 290; 290/5 = 58;