根据题意得, 1 A + 1 B + 1 C + 1 D = 1 8 ① 1 B + 1 C + 1 D + 1 E = 1 6 ② 1 A + 1 E = 1 12 ③ ①-②得, 1 A ? 1 E =? 1 24 ④,③+④得, 2 A = 1 24 ,解得A=48.所以A一个人单独干48天可完工.