On decreasing the price of a colour $TV$ by $30 \%$,its sale is increased by $20 \%$. The effect on the revenue is:

The length and breadth of a square are increased by $30 \%$ and $20 \%,$ respectively. The area of the rectangle so formed exceeds the area of the square by:

An empty fuel tank of a car was filled with an ordinary type of petrol. When the tank was one-third empty,it was filled with high-speed petrol. Again,when the tank was one-third empty,it was filled with an ordinary type of petrol. Again,when the tank was one-third empty,it was filled with high-speed petrol. At this time,what was the percentage of high-speed petrol in the tank?

The length of a rectangle increases by $20 \%$ and the breadth by $30 \%$. Then the perimeter of the rectangle will increase by:

The difference between a number and its two-fifth is $610$. What is $10\%$ of that number?

The population of a city is $20000$. It increased by $20\%$ during the first year and $30\%$ during the second year. The population after two years will be: