✔ 最佳答案
(1) 1 / (2/3) / (4/5/6)
= (3/2) / (4/30)
= (3/2)(30/4)
= 90/8
= 11.25
(2) (p + q + r + s)/4 = 62.5
p + q + r + s = 250 ... (1)
(p + r + s + t)/4 = 60
p + r + s + t = 240 ... (2)
(p + s + t)/3 = 55
p + s + t = 165 ... (3)
(q + s)/2 = 62.5
q + s = 125 ... (4)
(2) - (3) => r = 75
Sub into (1), p + q + 75 + s = 250
p + q + s = 175 ... (5)
(5) - (4) => p = 50
(3) 設乙能獨自在N小時完成工程
甲每小時完成工程的1/14
乙每小時完成工程的1/N
甲乙合作做了7小時後,乙獨力用了3小時 => (1/14 + 1/N) * 7 + (1/N)*3 = 1
1/2 + 7/N + 3/N = 1
10/N = 1/2
N = 20
乙獨力完成整件工程,需時20小時
(4) 設甲中3個(bca)則乙猜中1個,丙猜中0個,不符
設乙中3個(acd)則甲猜中1個,丙猜中2個,不符
設丙中3個(abd)則甲猜中0個,乙猜中2個,符合題意
c不能領獎