posted by chuck .
I have 28 marbles in all. Red,Blue, Green. 8 of them are blue. I have 3 times as many red marbles than green marbles. How many are red ?
if 8 marbles are blue then
28 - 8 = 20 are green and red marbles
then if we let x = the number of green marbles,
then the number of red marbles is 3 times the number of green marbles, or 3*x,, and their total sum must be 20:
x + 3*x = 20
combining similar terms,
4x = 20
now solve for x. then get the number of red marbles by multiplying it by 3.