If the cost of 10 books is ₹250, then find the cost of 15 books.

The average of five terms is 40. If the first four terms are given as 50, 52, 35 and 46, find the fifth term.

Two successive discounts of 20% and 30% are given while selling an article. What is the ratio of the marked price of the article to its selling price?

A boat takes 16 minutes and 24 minutes to cover a certain distance downstream and upstream, respectively. If the speed of the boat in still water is 15 km/h, find the speed of the stream.

What is the compound interest on ₹24,000 for 2 years at the rate of 10% per annum, if interest is compounded annually?

The average of 5 numbers, arranged in a row, is 309. The average of the first two of these numbers is 431 and the average of the last two of these numbers is 231.5. What is the value of the number at the center of the row?

A shopkeeper buys three products a, b, c and sells them at 20%, 30%, 40% profit, respectively. What is ratio of the selling price of these products, if the ratio of their cost prices is 4:3 :2?

The average of 21 consecutive natural numbers is 53. What is the value of the smallest of these 21 numbers?