Answer: The chemist needs to mix 25 milliliters of the 80% solution with 75 milliliters of the 40% solution to get 100 milliliters of a 50% solution.
Explanation:
Let x be the number of milliliters of 80% solution needed, and y be the number of milliliters of 40% solution needed.
From the first equation, we can write:
0.80x + 0.40y = 0.50(100)
Simplifying this equation, we get:
0.80x + 0.40y = 50
Dividing both sides by 0.20, we get:
4x + 2y = 250
From the second equation, we know that:
x + y = 100
Solving this equation for y, we get:
y = 100 - x
Substituting this expression for y into the first equation, we get:
4x + 2(100 - x) = 250
Simplifying this equation, we get:
2x + 200 = 250
Subtracting 200 from both sides, we get:
2x = 50
Dividing both sides by 2, we get:
x = 25
Substituting this value for x into the equation y = 100 - x, we get:
y = 75
Therefore, the chemist needs to mix 25 milliliters of the 80% solution with 75 milliliters of the 40% solution to get 100 milliliters of a 50% solution.