Let x and y be the number of red and blue marbles, respectively.
Since there are 12 more red marbles than blue ones, we have an equation:
x- y= 12 (1)
On the other hand, we also know that:
x+ y= 210 (2)
x- y= 12 (1)
x+ y= 210 (2)
Take (1)+ (2), we have:
(x- y)+ (x+ y)= 12+ 210
⇒ 2x= 222
⇒ x= 222/2
⇒ x= 111
There are 111 red marbles.
Hope this helps.
