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

The price of sugar has fallen by $10 \%$. How many quintals can be bought for the same money which was sufficient to buy $18$ quintals at the higher price?

$40 \%$ of $1640 + ? = 35 \%$ of $980 + 150 \%$ of $850$

In a company,there are $75\%$ skilled workers and the remaining are unskilled. $80\%$ of skilled workers and $20\%$ of unskilled workers are permanent. If the number of temporary workers is $126$,what is the total number of workers?

Water tax is increased by $20 \%$ but its consumption is decreased by $20 \% .$ Then the increase or decrease in the expenditure of the money is

In a certain school,$20 \%$ of students are below $8$ years of age. The number of students above $8$ years of age is $\frac{2}{3}$ of the number of students of $8$ years age,which is $48$. What is the total number of students in the school?