#3

The number of girls at Sky High School is 60 greater than the number of boys. If there are 1250 students all together, how many girls are there?

Let x = the # of girls
Let y = the # of boys

x + y = 1250 (y = 1250 - x)
y + 60 = x (y= x - 60)

Input it into your graphing calculator and you have your solution (almost). Good window settings are:
xmin = -10
xmax = -1500
ymin = -10
ymax = 1000

The solution is (655, 595), so there are 655 girls in Sky High School.