mixed powder ratios in a bag

Question

If you have 57 grams of substance A and 19 grams of substance B and 19 grams of substance C and 15 grams of substance D and 9 grams of substance E and you mix all of these powders perfectly in a bag and you then take a 4 gram serving size out of the already mixed bag how much of each substance would you have in milligrams of each substance from the 4 gram serving size?

Answer 1

Sum up the weights of each substance. Call that w

Multiply each substance's weight by (4 / w)