Question 319040
The ratio of red to the total is {{{R/(R+30)}}} where R is the number of red marbles.
{{{R/(R+30)=60/100}}}
{{{100R=60(R+30)}}}
{{{100R=60R+1800}}}
{{{40R=1800}}}
{{{R=45}}}
You need to have 45 marbles in the jar to have 60% red.
You currently have 10 marbles.
{{{N=45-10=35}}}
You need to add {{{highlight(35)}}} red marbles.