Explanation
To determine the average speed from a distancetime graph, follow these steps:
Identify Key Points
 Select two points on the distancetime graph where you'll calculate the average speed. These points should be given as $(t_1, d_1)$ and $(t_2, d_2)$, where:
 $t_1$ and $t_2$ represent the time coordinates.
 $d_1$ and $d_2$ represent the distance coordinates.
Calculate Time Interval

Compute the time interval $\Delta t$:
$\Delta t = t_2  t_1$
Calculate Distance Interval

Compute the distance interval $\Delta d$:
$\Delta d = d_2  d_1$
Average Speed Formula

Use the formula for average speed $\bar{s}$:
$\bar{s} = \frac{\Delta d}{\Delta t}$where:
$\Delta d = d_2  d_1$ $\Delta t = t_2  t_1$
Example Calculation
Let's consider a practical example:
 Suppose point $A$ is at $(2, 10)$ and point $B$ is at $(5, 40)$.

Identify key points:
 $t_1 = 2$, $d_1 = 10$
 $t_2 = 5$, $d_2 = 40$

Calculate time interval:
$\Delta t = 5  2 = 3 \, \text{hours}$ 
Calculate distance interval:
$\Delta d = 40  10 = 30 \, \text{kilometers}$ 
Calculate average speed:
$\bar{s} = \frac{30 \, \text{km}}{3 \, \text{hr}} = 10 \, \text{km/hr}$
Thus, the average speed of the object between points $A$ and $B$ is 10 km/hr.
By understanding these steps and applying the above formulas, you can easily calculate the average speed using a distancetime graph.