You will need
• pen, paper, analytical thinking
Instruction
1
Write the problem statement. 40% vinegar is 100%, you need to find how much to take of vinegar to obtain a 6% vinegar. It will be H. Recorded two par: 40%=100%, 6%=H.
2
We get the proportion: 40/6=100/x.

Multiply 6 by 100 and divide by 40.
3
Get vinegar essence is 15% of the total water and acetic solution.

It is possible to take 15 ml of vinegar and 75 ml of water to obtain approximately 100 ml of 6% vinegar. About - because water has the property of substitution, and withdrawal of different solutions may yield slightly less than originally planned.
4
The task is more difficult. Is buckwheat flour with a protein content of 12.6 g per 100 g of dry product. And there is a starch with a protein content of 1 g per 100 g of dry product. You need to make the starch-flour mixture with a protein content of 2 g per 100 g of dry product.
5
Take for x the starch content in the mixture in grams, (100-x) content of buckwheat flour in the mixture in grams.
6
Then 1*x/100 - how many grams of protein is necessary for starch 12,6*(100-x)/100 - how many grams of protein accounts for buckwheat flour.

The sum of these fractions is 2 g of protein per 100 g of the mixture.
7
After solving the equation, we find that to obtain a mixture with a content of 2 g of protein we need to take 91 g starch and 9 g of buckwheat flour.