Question 103295
Let x= the amt. of 70% columbian coffee that MUST be added


{{{10*90+70x=p*(x+10)}}}
{{{900+70x=px+10p}}}
{{{(70-p)x=10p-900}}}
{{{x=10p-900/(70-p)}}}


Therefore, {{{10p-900/(70-p)}}} pounds must be added