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?

What percent of $4 \text{ km}$ is $8 \text{ meters}$?

Rice is now being sold at $Rs. 30$ per $kg$. During last month,its rate was $Rs. 26$ per $kg$. Find by how much percentage must a family reduce its consumption to keep the expenditure fixed?

In an election between two candidates,one got $55 \%$ of the total valid votes,and $20 \%$ of the total votes were invalid. If the total number of votes was $7500$,what was the number of valid votes that the other candidate received?

$A, B, C$ are three students. $A$ got $18 \%$ more marks than $B$ and $12 \%$ less than $C$. If $B$ got $220$ marks,how many marks did $C$ get?

The population of a town is $123,456,789$. It increases by $10\%$ during the first year,$20\%$ during the second year,and $30\%$ during the third year. What is the average percentage increase during the three years?