题1 设男 = m,女 = f,总人数 = x m = (5/9)x - 4__i f = (2/5)x + 6__ii m + f = x m = x - f__iii 把 iii 放入 i, x - f = (5/9)x - 4 f = (4/9)x + 4__iv 用 iv - ii, 0 = (2/45)x - 2 (2/45)x = 2 x = 45
当地有45人。
题2 设第一天 = a,第二天 = b,总书页 = x
a = (1/8)x + 21__i b = (1/6)x - 6__ii a + b + 172 = x a = x - b - 172__iii 把 iii 放入 i, x - b - 172 = (1/8)x + 21 b = (7/8)x - 193__iv 用 iv - ii 0 = (17/24)x - 187 (17/24)x = 187 x = 264