Two pipes P and Q, when opened alone can fill the tank in 20 and 30 hours respectively. If both pipes are opened together, then in how many hours will the tank be filled?
The marked price of an article is Rs.1,280. If a shopkeeper sold the article at 12% profit after giving 30% discount, then the cost price of the article is:
A person invested Rs. 2,000 on simple interest for 7 years to obtain a total amount of Rs. 3,400 on a certain annual rate of interest. What was the rate of interest to obtain the above amount ?