I start with 24 oz.
If this is 15% iodine, then I have
(24)(0.15) = 3.6 oz iodine in the starting 24 oz.
I am going to add x oz of pure, 100%, iodine.
My final volume will be what I started with pus what I add:
24+x
The amount of iodine I will have in the final solution is the amt of iodine I started with, plus the pure iodine I add:
3.6+x
The percent wanted is 25%, or 25 per cent, or 25 per hundred.
so iodine/total = part/whole = 25/100 = (3.6+x)/(24+x)
Write these fractions up and down instead of slanted sideways and you will see that you can cross multiply and solve for x.
The trick to most word problems is to NOT try and see what equation you can shove the numbers into. It is to think through the story like it is really happening. Your common sense and life experience will show you what to do.
