Answer: approximately 43.0769 milliliters of solution
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Step-by-step explanation:
They don't specify what the chemical solution is, but let's say you had a mix of water and gold particles. If you had x ml of this chemical solution, then 0.30x of that is pure gold.
Dividing the amount of pure gold (0.30x) over the amount of solution (x) leads to 30%, so,
(0.30x)/x = 0.30
We want to add 280 ml of water. This will increase the amount of total solution (x) but will not change the amount of pure gold (0.30x)
So the fraction (0.30x)/x becomes (0.30x)/(x+280). We want this to be equal to 0.04 which is the 4% we're after.
We therefore need to solve this equation (0.30x)/(x+280) = 0.04
Let's do so
(0.30x)/(x+280) = 0.04
0.30x = 0.04(x+280)
0.30x = 0.04(x)+0.04(280)
0.30x = 0.04x+11.2
0.30x-0.04x = 11.2
0.26x = 11.2
x = 11.2/0.26
x = 43.076923076923 which is approximate
x = 43.0769 rounding to 4 decimal places
You can round however you want. I would ask your teacher about rounding instructions.