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

One fill pipe A takes 3 minutes more to fill the cistern than two fill pipes A and B opened together to fill it. Second fill pipe B takes $$ {21{1\over 3}}$$ minutes more to fill cistern than two fill pipes A and B opened together to fill it. When will the cistern be full if both pipes are opened simultaneously?

Find compound interest on Rs. 50000 at 12 % per annum for 6 months, compounded quarterly. 

The ratio of efficiency of Arun is to Chitra is 5:3. The ratio of number of days taken by Bala is to Chitra is 2:3. Arun takes 6 days less than Chitra, when Arun and Chitra complete the work individually. Bala and Chitra started the work and left after 2 days. The number of days taken by Arun to finish the remaining work is?

Mr. Khanna took a loan of Rs 10,000 on simple interest for two years at the rate 3% per annum. The total amount that he will be paying as interest in 2 year is 3% of his monthly salary. What his monthly salary?

The average age of a cricket team of 11 players is the same as it was 3 years back because 3 of the players whose current average age of 33 years are replaced by 3 youngsters. The average age of the new comers is: 

In how many different ways can the letters of the word 'NATIONAL' be arranged?

Aryan invested ₹ 5200 at 4 %, 6 % and 8 % per annum simple interest. At the end of the year, he got the same interest in all the three cases, find the money invested at 4%.