One business charges $12 per t-shirt custom made.Another business charges $11 per t-shirt plus a $20 set up fee for custom made.If you were to graph both of these scenarios on the coordinate plane, the first graph would be proportional and the second non proportional. How would you transform the first graph to make it become a non proportional graph with the same y-intercept as the second graph?

1 answer

To transform the first graph (which represents the business charging $12 per t-shirt) into a non-proportional graph with the same y-intercept as the second graph (which has a $20 setup fee), you need to introduce a fixed cost.

The equation for the first business can be expressed as:

\[ y = 12x \]

where \( y \) is the total cost and \( x \) is the number of t-shirts.

The equation for the second business can be expressed as:

\[ y = 11x + 20 \]

To make the first graph non-proportional while maintaining the same y-intercept of $20, you can add a fixed cost (setup fee) to the first equation. The result will be:

\[ y = 12x + 20 - 12(0) \] or simply, \[ y = 12x + 20 - 12x_0 \]

However, to clarify the transformation with a clear understanding of the y-intercept, you can modify it directly:

  1. Start with the original equation \( y = 12x \).
  2. Shift it vertically by adding a constant amount, in this case, \( 20 \).

So the transformed equation becomes:

\[ y = 12x + 20 \]

This new equation is non-proportional (due to the presence of the fixed cost) and has the same y-intercept (which is \( 20 \), the point where the graph intersects the y-axis).

In summary, by adding a fixed setup fee of $20 to the cost of custom t-shirts, you've successfully transformed the initial proportional graph into a non-proportional one, maintaining the same y-intercept.