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

$A$ person travels along a straight road for the first half time with a velocity $v_1$ and the next half time with a velocity $v_2$. The mean velocity $V$ of the man is

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

Which information cannot be drawn from average velocity?

The position of an object moving along the $X$-axis is given by $x = \alpha + \beta t^2$,where $\alpha$ and $\beta$ are constants with appropriate dimensions and $t$ is time in seconds. The average velocity between $t = 2 \ s$ and $t = 4 \ s$ is $12 \ m/s$. If $\alpha = 8 \ m$,then the value of $\beta$ is: (in $m/s^2$)

$A$ particle covers half of its total distance with speed $v_1$ and the rest half distance with speed $v_2$. Its average speed during the complete journey is