## Modelling Changenumber of dvds and blu-rays sold per year

I found the number of DVDs and Blu-Rays sold in millions on this website . As shown on the following graph, the number of DVDs sold since they were created in 1995 (although my data only starts in 1998) kept increasing until 2008, when the amount sold suddenly dropped despite the invention of the Blu-Ray in 2007. This was probably due to the fact that it became possible to watch movies without buying a physical copy of them, like on Netflix. The number of DVDs sold keeps dropping until the end of my data in 2015.

My graph: Number of DVDs and Blu-Rays sold per year (in millions)

I split my graph into three sections according to the data: first section, the rapid increase. Second section, the increase slows and third section, the data drops. Here are my data tables for each section.

Data Table Section 1
Data Table Section 2
Data Table Section 3
Here are my lines of best fit for each section of the graph

After splitting the graph into sections, I found the line of best fit for each. To do that, I put a ruler on my graph and found the place where the line should be approximately. Then I had to find the more accurate slope of the lines and their y intercepts. Only then could I graph the lines.

### here are my calculations:

#### Interval/section 1

Slope ≈ 28.6 and y intercept ≈ -24.6

#### Interval/Section 2

(a few steps are skipped since they were already shown in interval 1)

Slope ≈ 17.5 and y intercept ≈ 91.5

#### Interval/section 3

Slope ≈ -19.6 and y intercept ≈ 452.4

### Line of best fit

The long green curve is the line of best fit for the entire data set

I used a quadratic equation to find my line of best fit. At first, I wanted to use a linear equation because it was a better fit for section 3 of the graph and would therefore have given me more accurate predictions, however, it did not at all fit with sections 1 and 2, which have a positive correlation, so overall the curve is better. The data on my graph shows that in 2067, -6 700 million DVDs will be sold and in 2112, - 21 350 DVDs will be sold. Of course, this is not physically possible, so I've come to the conclusion that by 2067 there will be no more DVDs or Blu-Rays sold.

by Clara

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