Clacule os valores a e b, sabendo q a+b=30 e q a/b=4/5

A+b = 30 
a/b = 4/5 --> 5a = 4b --> a = 4b/5

4b/5 + b = 30
4b + 5b = 5*30
9b = 150
b = 150/9
b = 50/3

a+50/3 = 30
3a+50 = 90
3a = 90-50
3a = 40
a = 40/3

Verificando:
a/b = 4/5
(40/3) / (50/3) = 
(40/3)*(3/50) = 
40/50 = 
4/5 (V)
Logo:
a = 40/3 e b = 50/3​