Question 1187114
The physical part of the description is wrong;  a salt solution in water at ordinary room temperature is not higher than about 25 or 26 % salt.  
Even at very high water temperatures,  near boiling is needed to reach about 38%.  Your description did not say anything about conditions of temperature.


1 kg of main ingredient added to a mixture of main ingredient plus carrier material gave   33&1/3 percent main ingredient.
Understand as a basic fact that 33&1/3 percent is 33&1/3 parts per hundred, or the same as 1/3.  Since the entire description is based on mass,
this means  your mixture up to this point is  1 kg of the main ingredient, and 2 kg of the carrier material.  Those are THREE PARTS total by mass.
This means that the carrier material plus main ingredient at the beginning of the problem, HAD NO MAIN INGREDIENT.  It was only the carrier material.


The problem description continued.  
1 kg of carrier material was added to the mixture. 
The result will then be:


{{{mainIngredient/totalMassMixture}}}

{{{(1*kg)/(4*kg)}}}

{{{(1/4)}}}

{{{0.25}}}

25 PERCENT


This is NOT 30% as the description stated.

Fix your problem description.