Sample Problem This question comes from the third chapter of McConnell-Brue Economics. Explain the following news dispatch from Hull, England: "The fish market slumped today to what local commentators called 'a disastrous level' all because of a shortage of potatoes. The potatoes are one of the main ingredients in a dish that figures on almost every cafe menu--fish and chips." We can use the EconGraph Toolkit to create a diagram which shows the effect on the fish market of the potato shortage described in the question. First build a supply and demand diagram by clicking on the straight line button and placing a line on the XY axis. Grab one of the squares on the line and twist the line so it slopes downward. This will be the demand curve that existed before the potato shortage so grab it and drag it to upper right hand area of the XY axis. Second, click on the straight-line button again and position this line on the XY axis. This will be the supply curve so grab onto one of the little squares and make the line slope upward to the right. Now position this supply curve roughly in the center of the XY axis. Third, click on the straight line button once again and create a second demand curve. This will be the new demand curve that exists after the potato shortage. It should be positioned between the original demand curve and the origin of the XY axis. Fourth, we need to label the graph. Use the text tool to label the supply and demand curves. This is also where the button with the little square on it comes into play. Click on that button, then place the cursor over the intersection of the supply curve and the first demand curve. Now click and hold the mouse button and drag the cursor to the origin of the XY axis. This creates a dashed line showing the initial price and quantity in the fish market. You can use the text tool to label this price and quantity. Now follow the same procedure to label the price and quantity after the potato shortage. With these few simple steps you have created a supply and demand graph that can be printed out or sent in an e-mail to your professor. With a little practice, you can use this toolkit to create any graph you need in the principles course.