SOLUTION: How many cups of grapefruit juice must be added to 20 cups of a punch that is 10% grapefruit juice to obtain a punch that is 25% grapefruit juice? You will impress me extra, if you

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Question 608055: How many cups of grapefruit juice must be added to 20 cups of a punch that is 10% grapefruit juice to obtain a punch that is 25% grapefruit juice? You will impress me extra, if you include your work. Hint: you do not end with twenty cups of punch.
Found 2 solutions by scott8148, josmiceli:
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
(10%)(20) + x = (25%)(20 + x)

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Hope this is impressive
Let +x+ = cups of grapefruit juice that needs to be added
+.1%2A20+=+2+ = cups of grapefruit juice in 20 cups of 10% punch
( the part that isn't grapefruit juice might be water, but that
doesn't really matter )
----------------
+%28+x+%2B+2+%29+%2F+%28+x+%2B+20+%29+=+.25+
+x+%2B+2+=+.25%2A%28+x+%2B+20+%29+
+x+%2B+2+=+.25x+%2B+5+
+.75x+=+3+
+x+=+4+
You must add 4 cups of grapefruit juice
check:
+%28+4+%2B+2+%29+%2F+%28+4+%2B+20+%29+=+.25+
+6%2F24+=+.25+
+6+=+.25%2A24+
+6+=+6+
OK