Question 145486
Let {{{x}}}= pounds of extra-lean hamburger to be added
In words:
(pounds of fat in the extra-lean) + (pounds of fat in reg hamburger)
divided by total pounds of meat = 10% fat mixture
{{{(.07x + .15*30) / (x + 30) = .1}}}
multiply both sides by {{{x + 30}}}
{{{.07x + 4.5 = .1*(x + 30)}}}
{{{.07x + 4.5 = .1x + 3}}}
{{{.03x = 4.5 - 3}}}
{{{.03x = 1.5}}}
{{{x = 50}}}
50 lbs of extra-lean hamburger must be used 
check:
{{{(.07x + .15*30) / (x + 30) = .1}}}
{{{(.07*50 + .15*30) / (x + 30) = .1}}}
{{{(3.5 + 4.5) / (50 + 30) = .1}}}
{{{8 / 80 = .1}}}
{{{.1 = .1}}}
OK