If $2, x, 20$ are three consecutive terms of an $A.P.$,then $x = ..........$

Are $1, 3, 9, 27, \ldots$ in $AP$? If they form an $AP$,find the common difference $d$ and write three more terms.

$A$ small terrace at a football ground comprises of $15$ steps each of which is $50 \, m$ long and built of solid concrete. Each step has a rise of $\frac{1}{4} \, m$ and a tread of $\frac{1}{2} \, m$. Calculate the total volume of concrete required to build the terrace (in $m^3$).

In which of the following situations,does the list of numbers involved make an arithmetic progression,and why? The amount of money in the account every year,when ₹ $10000$ is deposited at compound interest at $8 \%$ per annum.

The angles of a triangle are in $AP$. The greatest angle is twice the least. Find all the angles of the triangle (in $^\circ$).

Do $4, 10, 16, 22, \ldots$ form an $AP$? If they form an $AP,$ write the next two terms.