If $90 \%$ of $A = 30 \%$ of $B$ and $B = x \%$ of $A$,then the value of $x$ is

What percentage of numbers from $1$ to $70$ have squares that end in the digit $1$?

Neha has a watch which gains $2 \%$ per hour when the temperature is in the range of $40^{\circ}C - 50^{\circ}C$ and it loses at the same rate when the temperature is in the range of $20^{\circ}C - 30^{\circ}C$. The watch runs on time in all other temperature ranges. On a sunny day,the temperature started rising from $8$ $a.m.$ at a uniform rate of $2^{\circ}C$ per hour and during the afternoon it started falling at the same rate. Find what time will it be by the watch at $7$ $p.m.$ if at $8$ $a.m.$ the temperature was $32^{\circ}C$ and at $4$ $p.m.$ it was $40^{\circ}C$?

The number of students in a class is increased by $20 \%$ and the number now becomes $66$. Initially,the number was:

$A$ student multiplied a number by $\frac{3}{5}$ instead of $\frac{5}{3}$. What is the percentage error in the calculation (in $\%$)?

Which one of the following shows the best percentage?