Question 126279
Let {{{p}}} = pounds of peanuts needed
Let {{{c}}} = pounds of cashews needed
{{{c = 70}}} given
In words:
(price of peanuts used)+(price of casews used)/(pounds of mixture) = price/pound
{{{(6p + 15c) / (p + c) = 13}}}
{{{(6p + 15*70) / (p + 70) = 13}}}
{{{6p + 1050 = 13p +  910}}}
{{{7p = 1050 - 910}}}
{{{7p = 140}}}
{{{p = 20}}} answer
20 pounds of peanuts should be used
check answer:
{{{(6p + 15c) / (p + c) = 13}}}
{{{(6*20 + 15*70) / (20 + 70) = 13}}}
{{{(120 + 1050) / 90 = 13}}}
{{{1170 / 90 = 13}}}
{{{13 = 13}}}
OK