Final answer:
To show a change on the demand curve for a soft drink after a price decrease from 3 to 2 dollars with demand increasing from 40 to 50 cans, plot the original and new price-quantity points and draw the curve through these points, demonstrating a move along the demand curve to a new higher demand point.
Step-by-step explanation:
To illustrate the change on a demand curve for the scenario where a shop decreases the price of a soft drink from 3 dollars to 2 dollars and sees an increase in the quantity demanded from 40 to 50 cans a day, we can draw a graph where the x-axis represents quantity and the y-axis represents price. Originally, at the $3 price point, the point on the demand curve would be at 40 cans (Q1). After the price reduction to $2, the quantity demanded increases to 50 cans (Q2). Thus, we would plot a new point at this lower price and higher quantity, and then draw a new demand curve passing through this point, showing that demand has increased.
In economics, this outcome is expected as per the law of demand, which states that there is an inverse relationship between price and quantity demanded, ceteris paribus. So, when the price decreases, the quantity demanded usually increases, causing a rightward shift in the demand curve. This action does not translate to a shift of the entire curve but instead moves along the curve to a new point, reflecting the changes in demand due to the price change.