An amount doubles itself in 5 years with simple interest. What is the rate of interest per year?

The marked price of a radio is Rs. 480. The shopkeeper allows a discount of 10% and still gains 8%. If no discount is allowed, find his gain percent.

The cost price of 10 articles is equal to the selling price of 9 articles. Find the profit percent.

If the height of a cylinder is increased by 15% and the radius of its base is decreased by 10%, then by what percent will its curved surface area change?

200 litres of mixture contains 15% water and the rest is milk. The  amount of milk that must be added so that the resulting mixture contains 87.5 % milk is:

The ratio between the ages of a father and his son four year ago was 19:6. If the difference between the ages of the father and son is 26 years, what will be the ratio of their present ages?

A motor car finishes a journey in 10 hours. The first half at 21 km/hr. and the rest at 24 km/hr. Find the distance?

Two pipe can fill a cistern in 3 hours and 4 hours respectively and a waste pipe can empty it in 2 hours. If all  the three pipes are kept open, then the cistern will be filled in