SOLUTION: Can someone please help me? A butcher has some hamburger that is 21% fat and some that is 15% fat. How many pounds of each should be mixed to make 84 pounds of hamburger that is 17

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Question 28998: Can someone please help me? A butcher has some hamburger that is 21% fat and some that is 15% fat. How many pounds of each should be mixed to make 84 pounds of hamburger that is 17% fat?
Thank You.
Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
Let x = amount of 21%fat hamburger

Now for the trickiest part...
how much of the 15%fat hamburger is there?
answer is "the rest of the 84lb", so this is (84-x)

The rest is just about BEFORE = AFTER since you add the BEFORE together to get the AFTER.

BEFORE
xlb of 21% + (84-x)lb of 15%
0.21x + 0.15(84-x)
0.21x + 12.6 - 0.15x
0.06x + 12.6

AFTER
84lb of 17%
0.17*84
14.28

so, 0.06x + 12.6 = 14.28
0.06x = 1.68
x = 1.68/0.06
x = 28lb

so we need 28lb of the 21% fat and 56lb of the 15% fat.

jon.