SOLUTION: How many grams of salt must be added to 90 grams of a 20% salt solution to make a 25% salt solution? I can't seem to figure out the formula. I tried x+90(.20)=0.25 and various

Question 861253: How many grams of salt must be added to 90 grams of a 20% salt solution to make a 25% salt solution?
I can't seem to figure out the formula. I tried x+90(.20)=0.25 and various variations, but I just can't get the formula to work. I would appreciate your help to at least get the equation.
Found 2 solutions by josgarithmetic, richwmiller:
Answer by josgarithmetic(39629) (Show Source): You can put this solution on YOUR website!
A thorough lesson on this type of exercise problem is in this link:

two-part mixture for known final concentration and one part known but other part unknown.
http://www.algebra.com/tutors/Two-Part-Mixture-with-one-material-quantity-unknown.lesson?content_action=show_dev

I believe you were or are missing a denominator expression representing the total amount of resulting solution. What you showed in your equation is a quantity of salt as expression, and a fraction of salt for resulting solution.

Study the lesson; but also understand that concentration is a ratio like this:
(amount of solute)/(amount of solution containing the solute).
You want this RATIO to be 0.25 if keeping with decimal fractions; or 25 if keeping with percentage concentration units.

Final answer seems to be 6 grams. This result checks.
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
.20*90+x=.25*(90+x)
18+x=22.5+.25x
.75x=4.5
x=6

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