因为甲乙两数的比是4 :7
所以设 甲 = 4x ,乙 = 7x
(4x + 20) :(7x - 20) = 5 :6
6(4x + 20) = 5(7x - 20)
24x + 120 = 35x - 100
35x - 24x = 120 + 100
11x = 220
x = 220 ÷ 11
x = 20
甲 = 4x = 80
乙 = 7x = 140