SOLUTION: How many grams of salt need to be added to 60 grams of a 20% salt solution in order to increase the salt content to 25%? I tried this question on one of my tests.. I failed the

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Question 570766: How many grams of salt need to be added to 60 grams of a 20% salt solution in order to increase the salt content to 25%?
I tried this question on one of my tests.. I failed the test because these types of problems were half the test.. I do not know how to do it. The answer is apparently four. I just need to know how to do it.
Thank you!
Answer by Maths68(1474) About Me  (Show Source):
You can put this solution on YOUR website!
Solution A
Amount = x grams
Concentration =100% =1 (It is pure salt)
Solution B
Amount = 60 grams
Concentration =20% = 0.2
Resultant Solution
Amount = (60+x) grams
Concentration =25%=0.25
[Amount Solution A * Concentration A] + [Amount Solution B * Concentration of B] = Amount of Resultant * Concentration of resultant
(x)(1)+(60)(0.2)=(60+x)(0.25)
x+12=15+0.25x
x-0.25x=15-12
0.75x/0.75=3/0.75
x=4


We need to add 4 grams of salt to increase the salt content to 25%