A bag contains white marbles and red marbles, 16 in total. The number of white

marbles is 4 less than 3 times the number of red marbles. How many white marbles

are there?

11

Step-by-step explanation:

Let's call the white marbles w and the red marbles r. We can write:

w + r = 16 (1)

w = 3r - 4 (2)

3r - 4 + r = 16 (3) (Substitute (2) into (1))

4r = 20 (simplify)

r = 5 (divide by 4) which means w = 16 - 5 = 11