The system would be:
x + y = 27
y = 2x
How to write the system?
Let's define the variables x = number of boys and y = number of girls.
The first equation states that the total number of boys and girls is 27.
x + y= 27
The second equation states that the number of girls is twice the number of boys.
y = 2x
Then the system that represents this situation is:
x + y = 27
y = 2x