A person borrows some money for 4 years at the rate of simple interest. If the ratio of principal and total interest is 5 : 1, then what is the rate ( in percentage) of interest?
The simple and compound interest that can be earned in two years at the same rate is Rs 4000 and Rs 4180 respectively. What is the rate (percent per annum) of interest?
If a taxi going at 40 km/hr takes 25 minutes to travel a certain distance, by how much should it increase its speed (in km/hr) to travel the same distance in 20 minutes?