Question 712337
u = how many ounces of pure bran


{{{(100u+70*42)/(u+70)=59.4}}}


{{{100u+70*42=59.4(u+70)}}}
{{{100u+70*42=59.4u+59.4*70}}}
{{{100u-59.4u=59.4*70-42*70}}}
{{{(100-59.4)u=(59.4-42)70}}}
{{{u=70(59.4-42)/(100-59.4)}}}

{{{u=30}}}
Add 30 ounces of pure bran to the 70 ounces of 42% bran to get 59.4% bran.