A scientist has acid solutions with concentrations of 4% and 15%. He wants to mix some of each solution to get 44 milliliters of solution with a 12% concentration. How many milliliters of each solution does he need to mix together?​

Let x and y be the amounts (in mL) of the 4% and 15% solutions, respectively, that the scientist needs to use.

He wants to end up with a 44 mL solution, so

x + y = 44 mL

Each milliliter of 4% solution contains 0.04 mL of acid, while each mL of 15% contains 0.15 mL of acid. The resulting solution should have a concentration of 12%, so that each mL of it contains 0.12 mL of acid. Then the solution will contain

0.04x + 0.15y = 0.12 × (44 mL) = 5.28 mL

of acid.

Solve for x and y. In the first equation, we have y = 44 mL - x, and substituting into the second equation gives

0.04x + 0.15 (44 mL - x) = 5.28 mL

0.04x + 6.6 mL - 0.15x = 5.28 mL

1.32 mL = 0.19x

x ≈ 6.95 mL

==>   y ≈ 37.05 mL

there are 70 more legs than eyes at the dog show (196 – 126 = 70). dogs have two more legs than eyes, and humans have the same number of legs as eyes. thus 70 is twice the number of dogs at the show, so the number of dogs is half of 70, which is 35. to get the number of humans, subtract 35 from 63: 63 – 35 = 28.

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