Why do we have to take $0$ for sugar instead of $100$ in this mixture?

Question

I recently took a look at the bucket method for mixture word problems. The image has been attached as seen below.

Imagine you have $300$ gram flour-sugar mixture that has $\% 30$ of flour and $\frac{1}{3}$ of this mixture is poured. Then, you readd the sugar as amount of poured flour-sugar mixture, which is $\frac{1}{3}$. Thereby, our equation is

$$200\cdot 30 + 100\cdot100 = 300 x$$

Which seems wrong because I took $100$ for sugar instead of $0$ according to the image. Why? Sugar is a pure substance, so it will be $100$ instead of $0$. Where am I going wrong?

Answer 1

Original mixture: $300 g$.

Pour out $\frac 13$. $300g\times \frac 13 = 100g$. We remove $100g$. $300g - 100g = 200g$. We have $200 g$ of mixture.

The mixture is $30\%$ flour and $100\% - 30\% = 70\%$ sugar. So we have $200g\times 30\% = 60g$ of flour and $200g \times 70% = 140g$ of sugar.

We add $100$ grams of pure sugar.

So we have $200g\times(100\% - 30\%) + 100g\times 100\% =$

$200g\times 70\% + 100g\times 100\% = $

$140g + 100g = 240g$ of sugar.

And we have $200g + 100g$ of mixture.

So the new mixture is $\frac {240}{300} = 80\%$ sugar.

.....

The $0$ percent would be if we added water. But we added sugar. Not water.