Question 127483
Let {{{b}}} = pounds of brazil nuts
Let {{{w}}} = pounds of walnuts
In words:
(price per pounds of brazil nuts)x(pounds of brazil nuts)
+ (price per pound of walnuts)x(pounds of walnuts)
divided by
(pounds of mixture) = price per pound of mixture
{{{b + w = 30}}}
{{{w = 30 - b}}}
{{{(5b + 3.5w) / 30 = 4}}}
{{{5b + 3.5w = 120}}}
{{{5b + 3.5*(30 - b) = 120}}}
{{{5b + 105 - 3.5b = 120}}}
{{{1.5b = 15}}}
{{{b = 10}}}
{{{w = 30 - 10}}}
{{{w = 20}}}
10 pounds of brazil nuts and 20 pounds of walnuts are needed
check:
{{{5b + 3.5w = 120}}}
{{{5*10 + 3.5*20 = 120}}}
{{{50 + 70 = 120}}}
{{{120 = 120}}}
OK