Question 981511
n jelly beans, none black, originally in the jar.


Added 90 black beans and mixed;
removed 120 beans and counted 18 black beans.


Concentration of black jelly beans is near {{{18/120}}}.


Quantity of jelly beans after the addition and mixing became n+90.


{{{highlight_green(90/(n+90)=18/120)}}}
If this equation makes sense, then all needs to be done now is solve for n.
The focus in this proportion equation is the comparison of concentrations of
the black jelly beans.