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

Out of his total income,Mr. Kapur spends $20 \%$ on house rent and $70 \%$ of the rest on household expenses. If he saves $₹ 1,800$,what is his total income?

In Convent Model School,$60 \%$ of the students are boys. In an aptitude test,$80 \%$ of the girls scored more than $40$ marks (out of a maximum possible $150$ marks). If $60 \%$ of the total students scored more than $40$ marks in the same test,find the fraction of the boys who scored $40$ marks or less?

$60 = ? \% \text{ of } 400$

$A$ man spends $75 \%$ of his income. His income increases by $20 \%$ and his expenditure also increases by $10 \%$. The percentage of increase in his savings is (in $\%$)

What percentage of numbers from $1$ to $70$ have squares that end in the digit $1$?