Sixty-five percent of a number is $21$ less than four-fifth of that number. What is the number?

In an election between two candidates,$10 \%$ of the voters did not cast their vote. $10 \%$ of the votes polled were found invalid. The successful candidate received $54 \%$ of the valid votes and won by a majority of $1620$ votes. The total number of voters enrolled on the voter's list was:

$88 \%$ of $370 + 24 \%$ of $210 - ? = 118$

The average monthly salary of all the employees in a factory is $Rs$ $8840$. If the average salary of all the officers is $Rs$ $15000$ and that of the remaining employees is $Rs$ $8000$,then what is the percentage of the officers among the employees?

The population of a town $2$ years ago was $62500$. Due to migration to big cities,it decreases every year at the rate of $4\%$. The present population of the town is:

Pradeep invested $20\%$ more than Mohit. Mohit invested $10\%$ less than Raghu. If the total sum of their investment is $₹ 17,880$,how much amount did Raghu invest?