Final answer:
To solve this problem, set up a system of equations using the method of mixture. The scientist should mix 70 mL of the 30% solution and 35 mL of the 80% solution to make a 60% solution.
Step-by-step explanation:
To solve this problem, we can set up a system of equations using the method of mixture. Let's denote the volume of the 30% solution as x mL and the volume of the 80% solution as y mL.
From the problem, we have the following two equations:
x + y = 35 (equation 1)
0.30x + 0.80y = 0.60(x + y) (equation 2)
We use equation 1 to express y in terms of x: y = 35 - x.
Substituting this value of y in equation 2, we get:
0.30x + 0.80(35 - x) = 0.60x + 0.60(35 - x)
Simplifying the equation:
0.30x + 28 - 0.80x = 21 + 0.60x
0.10x = 7
x = 70
Now, substitute the value of x back into equation 1 to find y: y = 35 - x = 35 - 70 = -35.
Since negative volume doesn't make sense, we discard the negative value. Therefore, the scientist should mix 70 mL of the 30% solution and 35 mL of the 80% solution to make a 60% solution.