A boy added all natural numbers from 1 to 10, however, he added one number twice due to which the sum becomes 58. What is the number which he added twice? 

A number increased by   $$22{1 \over 2}\%$$ gives 98 as result. The number is: 

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

The average of the marks obtained in an examination by 8 students was 51 and by 9 other students was 68. The average marks of all 17 students was: 

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%. 

A piece of land came to a person through three middlemen each gaining 20%. If the person purchased the land for Rs. 3,45,600 the original cost of the land was: 

What should come in place of the question mark (?) in the following question?
24% of 420 × 50% of 74 = ?