We know that the total number of girls plus the total number of boys equals 680. Let’s use G to represent girls and B to represent boys. Now let’s assign values to G amd
B. B=B G=B+40 Now add together B+B+40=680
2B+40=680
-40 -40
2B=640
/2 /2
B=320
If there are 680 students, and 320 are boys, there must be 360 girls.