A+b+с = 100
(3a/4) : (3b/2) : (3c/5) = 3:9:4
(a/4):(b/2) = 1/3
a/(2b) = 1/3
a = 2b/3
(b/2):(c/5) = 9/4
5b/(2c) = 9/4
9c = 10b
с = 10b/9
(2b/3) + b + (10b/9) = 100
6b+9b+10b = 900
25b = 900
b = 36
a = 2*36/3 = 2*12 = 24
с = 10*36/9 = 10*4 = 40
Проверка: 3a/4 = 18 3b/2 = 54 3c/5 = 24
отношение: 3: 9: 4