Why can the speed of a moving object never be negative?

Consider a particle moving along a straight line, whose position as a function of time is given by $s(t) = \alpha t^2 - \beta t + \gamma$, where $\alpha = 1 \text{ ms}^{-2}$, $\beta = 6 \text{ ms}^{-1}$ and $\gamma = 5 \text{ m}$. The average speed of the particle, in $\text{ms}^{-1}$, from $t = 0$ to $t = 6 \text{ s}$ is :

Is the average of different speeds called average speed? Do you agree?

Give the difference between average speed and average velocity.

$A$ bus travels the first one-third distance at a speed of $10\; km/h$,the next one-third at $20\; km/h$,and the last one-third at $60\; km/h$. The average speed of the bus is ........ $km/h$.

The velocity of an object moving in a straight line path is given as a function of time by $v = 6t - 3t^2$,where $v$ is in $m/s$ and $t$ is in $s$. The average velocity of the object between $t = 0$ and $t = 2 \ s$ is