Question 765318
The problem needs just one variable.
Let p = the number of pounds of Sumatran coffee to add to the Kona beans.


You want the resulting blend to be 65% Kona.


{{{50*100/(50+p)=65}}}
Adding p pounds of Sumatra coffee will reduce the concentration of Kona in the blend from 100% down to whatever concentration is desired.
SOLVE FOR p.


{{{5000=65(p+50)}}}
{{{5000=65p+3250}}}
{{{65p=5000-3250}}}
{{{65p=1750}}}
{{{p=26&12/13}}} pounds, but some judgement should be made here about what is most practical.  Best would be to bring that fraction down just a little bit, say make it to about {{{7/8}}} of a pound to ensure at least 65% Kona.  Say {{{highlight(p=26&7/8)}}} pounds.