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**ThePerfectHacker** Problem 2:

Let $\displaystyle x,y$ be the amout of weedkiller solution for 5% and 15% respectively.

Thus, he want to make 100 thus,

$\displaystyle x+y=100$

Now for the second part since the first solution has 5% the amount of actual weedkiller is $\displaystyle .05x=\frac{1}{20}x$ similarily the amount of actual weekiller for the second one is $\displaystyle .15y=\frac{3}{20}$.

Now he mixes them in such a way that he has 12% of weedkiller thus, there are

12%(100) of actual weedkiller thus, 12. Thus, the two equations are:

$\displaystyle x+y=100$

$\displaystyle \frac{1}{20}x+\frac{3}{20}y=12$

Multiply the second by 20 thus,

$\displaystyle x+y=100$

$\displaystyle x+3y=240$

From the second subtract the first,

$\displaystyle 2y=140$

Thus, $\displaystyle y=70$ of 15% solution.

Thus, $\displaystyle x=30$ of 5% solution.