Question

A boy added all natural numbers from 1 to 20. However he added one number twice, due to which the sum becomes 215. What is the number which he added twice?

• A. 5
• B. 8
• C. 7
• D. 11

Answer 1

Answer:

A. 5

Let, the number he added twice = x Sum of all natural numbers from 1 to 20, = 20 × (20 + 1)/2 = 10 × 21 = 210 210 + x = 215 x = 5