In a class of $80$ students,each student got sweets that are $15 \%$ of the total number of students. How many sweets were there?

Two numbers are $10\%$ and $25\%$ lesser than a third number. By what percentage must the second number be increased to make it equal to the first number (in $\%$)?

Two numbers are $50 \%$ and $80 \%$ less than a third number. By what percentage must the second number be increased to make it equal to the first number?

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

Two numbers are respectively $12 \frac{1}{2} \%$ and $25 \%$ more than a third number. The first number is what percentage of the second number?

If the height of a triangle is decreased by $40 \%$ and its base is increased by $30 \%$,what will be the effect on the area?