A bag contains green marbles and blue marbles, 24 in total. The number of green marbles is 9 less than 2 times the number of blue marbles. How many green marbles are there?

13

Step-by-step explanation:

A bag contains green marbles and blue marbles, 24 in total: g + b = 24

The number of green marbles is 9 less than 2 times the number of blue marbles: g = 2b - 9

Substitute g = 2b - 9 into g + b = 24

2b-9+b=24

3b=24+9=33

b=11

Substitute b = 11 into g = 2b - 9

g=22-9 = 13