$3.5$ can be expressed in terms of percentage as

In a class of $80$ students and $5$ teachers,each student received sweets equal to $15 \%$ of the total number of students,and each teacher received sweets equal to $25 \%$ of the total number of students. How many sweets were there in total?

The length of a rectangle is increased by $30 \%$ and the breadth by $20 \%$. Then the perimeter of the rectangle will increase by what percent?

In an examination,it is required to multiply a number by $7$,but by mistake,a student divides it by $7$. What is the error percentage?

Aditya's salary was increased by $40 \%$ and then decreased by $25 \%$. Find the net effect on Aditya's salary.

Depreciation applicable to an equipment is $20 \%$. The value of the equipment $3$ years from now will be less by: (in $\%$)