Find the value of the vehicle's speed (in km/h) between points B and C in the given graph.

(Note: In X-axis the value of time is given in “a.m.”)

The value of the vehicle's speed between points B and C in the given graph is $30\mathit{ km}/h$.
The Formula for Calculating Speed
Speed $=\frac{\mathit{Distance}}{\mathit{Time}}$ So, we need to calculate the distance first. Distance travelled by the vehicle between points B and C is given as
Total distance travelled at point C - Total distance travelled at point B
∴ Distance travelled $=40-30$
                                  $=10\mathit{ km}$
Now, we need to calculate the time taken by the vehicle. At point C, the time is 11:00 am and at point B the time is 10:40 am. Therefore, the time taken by vehicle to travel from B to C is $20\mathit{ min}$
∴ Time Taken $=\frac{20}{60}\mathit{ h}$
                        $=\frac{1}{3}\mathit{ h}$
∴ Speed $=\frac{\mathit{Distance}}{\mathit{Time}}$
              $=\frac{10}{\frac{1}{3}}\mathit{ km}/h$               $=30\mathit{ km}/h$
Hence, the speed of the vehicle between points B and C is $30\mathit{ km}/h$.