SOLUTION: Please help me solve this word problem I don't understand. Show an equation and a solution for the problem. Arnold needs a 25% solution of nitric acid. He has 20 ml of a 30% s

Question 508420: Please help me solve this word problem I don't understand.
Show an equation and a solution for the problem. Arnold needs a 25% solution of nitric acid. He has 20 ml of a 30% solution. How many ml of a 15% solution should he add to obtain the required 25% solution?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Show an equation and a solution for the problem. Arnold needs a 25% solution of nitric acid. He has 20 ml of a 30% solution. How many ml of a 15% solution should he add to obtain the required 25% solution?
--------------------------
Equation:
acid + acid = acid
0.30*20 + 0.15x = 0.25*(20+x)
----
Multiply thru by 100 to get:
30*20 + 15x = 25*20 + 25x
10x = 5*20
x = 10 ml (amt. of 15% solution needed)
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Cheers,
Stan H.
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