Question

To get a 100 kilograms of a 48% fat content chocolate how many kilograms of a 30% and 50% mix should be used

Answer 1

a kilogram %30 chocolate,
b kilogram %50 chocolate,
a+b = 100 kilogram chocolate,

48.(a+b) = 30.a + 50.b
48a + 48b = 30a + 50b
18a = 2b
b = 9a

a+b = a + 9a = 10a = 100 kg
a = 10 kg
b = 9.a = 90 kg

You should use,

10 kg %30 chocolate,
90 kg %50 chocolate