Crotonyl alcohol is an example of

The locus of the poles of focal chords of the parabola $y^2 = 4ax$ is

$A$ three-digit number $n$ is such that the last two digits are equal and differ from the first digit. The number of such $n$'s is:

The number of ways that $8$ beads of different colours can be strung as a necklace is

Find the missing numbers in the following factorization tree:

$A$ transistor is used as a common emitter amplifier with a load resistance of $2 \ k\Omega$. The input resistance is $150 \ \Omega$. Base current is changed by $20 \ \mu A$,which results in a change in collector current by $1.5 \ mA$. The voltage gain of the amplifier is