A car is worth £500 and loses £80 in value each month. How do you plot the car’s value over the first 5 months on a graph?

What the graph needs to show

You are modeling a steady monthly decrease in value, so the graph should be a straight line that starts at £500 and drops by £80 each month.

Make a value table for months 0 to 5

Start at month $0$ (the initial value) and subtract £80 each month:

• $m=0$: $V=500$
• $m=1$: $V=500-80=420$
• $m=2$: $V=500-160=340$
• $m=3$: $V=500-240=260$
• $m=4$: $V=500-320=180$
• $m=5$: $V=500-400=100$

Plotting points and drawing the line

1. Label the horizontal axis as months ($m$), from 0 to 5.
2. Label the vertical axis as value in pounds (£), covering at least 0 to 500.
3. Plot the coordinate pairs: $(0,500)$, $(1,420)$, $(2,340)$, $(3,260)$, $(4,180)$, $(5,100)$.
4. Use a ruler to draw a straight line through the points.

Equation of the line (optional but helpful)

The starting value is 500 (the intercept) and the change is $-80$ per month (the gradient), so:

$$V = 500 - 80m$$

Quick check

From month 0 to month 1, the graph should drop from 500 to 420, a decrease of 80. Every 1 month step should drop by the same amount.