A bag contains yellow marbles and red marbles, 16 in total. The number of yellow marbles is 1 more than 2 times the number of red marbles. How many yellow marbles are there?

11 yellow marbles

Step-by-step explanation:

Let y = yellow marbles

r = red marbles

There are 16 total marbles

y+r = 16

the number of yellow marbles is 1 more than twice the red marbles

y = 2r+1

Taking y+r = 16 and solving for r

r = 16-y

Substituting this into the second equation

y = 2 (16-y) + 1

Distribute

y = 32 - 2y + 1

Add 2y to each side

y + 2y = 32 - 2y + 2y+1

3y = 33

Divide each side by 3

3y/3 = 33/3

y = 11

There are 11 yellow marbles