If the price of apple increases from $Rs$ $80$ per $kg$ to $Rs$ $100$ per $kg$,by what percent should a person decrease the consumption of apple so that his expenditure remains the same (in $\%$)?

$A, B$ and $C$ start a business by investing $Rs. 70000$ that earns them a profit of $Rs. 42000$ at the end of the year. $A$ invests his share in the profit in a scheme that gives $10\%$ interest compounded annually and $B$ invests his share in a scheme that gives $20\%$ interest compounded annually. $A$ gets $Rs. 2520$ as interest at the end of $2$ years and $B$ gets an interest of $Rs. 4200$ at the end of one year. Find $C$'s investment in the business.

An ore contains $23 \%$ copper. To get $69 \text{ kg}$ of copper, the quantity of the ore required is: (in $\text{ kg}$)

The income of a company increases $20 \%$ per annum. If its income is $Rs$ $42664000$ in the year $1999$,what was its income in the year $1997$?

Rita invested $25 \%$ more than Sunil. Sunil invested $30 \%$ less than Abhinav,who invested $Rs$ $6,000$. What is the ratio of the amount that Rita invested to the total amount invested by all of them together?

Aman gave $40 \%$ of the amount he had to Rohan. Rohan in turn gave one-fourth of what he received from Aman to Sahil. After paying $₹ 200$ to the taxi driver out of the amount he got from Rohan,Sahil now has $₹ 600$ left with him. How much amount did Aman have?