SOLUTION: Dave has 20 ounces of a 20% of salt solution, How much salt should he add to make it a 25% solution?

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Question 425514: Dave has 20 ounces of a 20% of salt solution, How much salt should he add to make it a 25% solution?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let x = the ounces of salt he needs to add
given:
He has +.2%2A20+=+4 ounces of salt in solution now
In words:
( ounces of salt in final solution)/(total ounces in final solution) = % salt
-------------
+%28+x+%2B+4%29%2F%28+x+%2B+20%29+=+.25+
+x+%2B+4+=+.25%2A%28+x+%2B+20+%29+
+x+%2B+4+=+.25x+%2B+5+
+.75x+=+1+
+x+=+4%2F3+
He needs 1.333 ounces of salt
check:
+%28+x+%2B+4%29%2F%28+x+%2B+20%29+=+.25+
+%28+1.333+%2B+4%29%2F%28+1.333+%2B+20%29+=+.25+
+5.333%2F21.333+=+.25+
+.249988+=+.25+
error due to roundoff