Question : A boy added all natural numbers from 1 to 12, but he added one number twice, due to which the sum became 80. What is the number that he added twice?
Option 1: 3
Option 2: 2
Option 3: 7
Option 4: 8
Correct Answer: 2
Solution : Sum of the first $n$ natural numbers = $\frac{n(n + 1)}{2}$ Sum of the first 12 natural numbers = $\frac{12(12 + 1)}{2}$ = $\frac{12\times 13}{2}$ = 78 A number is added twice so that the sum becomes 80. The number added twice is (80 – 78) = 2 Hence, the correct answer is 2.
Result | Eligibility | Application | Selection Process | Cutoff | Admit Card | Preparation Tips
Question : A boy added all-natural numbers from 1 to 20. However, he added one number twice, due to which the sum became 215. What is the number which he added twice?
Question : The sum of three consecutive natural numbers divisible by 3 is 45. The smallest number is:
Question : The average of some natural numbers is 15. If 30 is added to the first number and 5 is subtracted from the last number, the new average becomes 17.5. What is the total number of natural numbers?
Question : Which one of the following is a factor of the sum of the first twenty-five natural numbers?
Question : The product of two numbers is 24 times the difference between these two numbers. If the sum of these numbers is 14, the larger number is:
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile