The price of onions has been increased by $50 \%$. In order to keep the expenditure on onions the same,the percentage of reduction in consumption has to be:

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

$A$ pharmaceutical company received $Rs. 3$ million in royalties on the first $Rs. 20$ million in sales of the generic equivalent of one of its products and then $Rs. 9$ million in royalties on the next $Rs. 108$ million in sales. By approximately what percent did the ratio of royalties to sales decrease from the first $Rs. 20$ million in sales to the next $Rs. 108$ million in sales?

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

In an examination,$30 \%$ and $35 \%$ students respectively failed in History and Geography while $27 \%$ students failed in both the subjects. If the number of students passing the examination is $248$,find the total number of students who appeared in the examination.

The weights of two iron balls are $3.5 \text{ kg}$ and $7.5 \text{ kg}$. What is the percentage weight of the first ball with respect to the second ball?