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

In an election between two candidates,$60 \%$ of the voters cast their vote,out of which $4 \%$ of the votes were declared invalid. $A$ candidate received $7344$ votes,which were $75 \%$ of the total valid votes. Find the total number of votes enrolled in the election.

The price of a shirt is increased by $15 \%$ and then reduced by $15 \%$. The final price of the shirt

Starting with $8000$ workers,the company increases the number of workers by $5 \%$,$10 \%$,and $20 \%$ at the end of the first,second,and third year,respectively. The number of workers in the fourth year is:

$34.5 \% \text{ of } 1800 + 12.4 \% \text{ of } 1500 = (?)^3 + 78$

Amit's monthly income is $30 \%$ more than that of Raunaq. Raunaq's monthly income is $20 \%$ less than that of Deepak. If the difference between the monthly incomes of Amit and Deepak is ₹ $800$,what is the monthly income of Raunaq?