Solution
For this case we know that the total of students are 396 so we can do this:
x + y = 396
Where:
x= number of girls
y = number of boys
Then we have the following condition:
4x = 7y
Then solving for x we got:
x = 7/4 y
Replacing in the first equation we got:
7/4 y + y = 396
11/4 y= 396
y= 396*4/11 = 144
And x= 7/4 * 144 = 252
Then the answer would be:
252 girls and 144 boys
