Jamie ordered 200 business cards and paid $23. She ordered 500 business cards a few months later and paid $35. Write and solve a linear equation to find the cost to order 700 business cards.
The 2-point form of the equation for a line is useful for this. It tells you .
y = (y2 -y1)/(x2 -x1)(x -x1) +y1
for a line through (x1, y1) and (x2, y2).
The points we are given are (200, 23) and (500, 35). We want to find the value of y for x=700. Putting all those numbers into the above equation gives ...
y = (35 -23)/(500 -200)(700 -200) + 23 . . . . . the linear equation
