Mixture Math Problem Help

I am having trouble setting these problems up! THANKS SO MUCH!

1) Andrew wants to mix a 25% solution of iodine with a 40% solution of iodine to make 32 ounces of a 30% solution. Rounded to the nearest tenth, how many ounces of the 25% solution will he need to use?


2) Duk Yon wants to mix a 20% saline solution with a 12% saline solution to make 40 ounces of a solution that is 15% saline. How many ounces of 12% saline solution will he need?

3) Akili wants to mix a 15% acid solution with a 40% acid solution to make 10 ounces of a 25% acid solution. How many ounces of the 40% acid solution will he need?

These three problems are similar, so I'll do the first one and then you can try the other two.

1) Let x = number of ounces of 25% solution.

Since the total amount of mixture is 32 ounces,
32 - x = number of ounces of 40% solution.

The number of ounces of iodine in the 25% solution is 0.25x.
The number of ounces of iodine in the 40% solution is 0.4(32 - x).
The total number of ounces of iodine in the 30% solution mixture is 0.3(32).

Therefore, we have

0.25x + 0.4(32 - x) = 0.3(32)
25x + 40(32 - x) = 30(32)
25x + 1280 - 40x = 960
320 = 15x
x = 320/15 = 64/3, or about 21.3 .

He will need to use about 21.3 ounces of the 25% solution.

Lord bless you today!

dk