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?
A5
B8
C7
D11
Answer:
A. 5
Read Explanation:
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
