Question 28998
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.