A student in a class wrote down the first n natural numbers and calculated their sum. While calculating the sum, he forgot to add two consecutive numebers and got the sum as 7,370. Find the two numbers that she forgot to add.
Explanation:
Sum of first n natrual numbers = n(n + 1)/2
The least value of n for which the sum is greater 7370 is 121.
∴ The sum of all the numbers should have been (121 × 122)/2 = 7381
∴ The sum of two consecutive numbers that she missed = 7381 - 7370 = 11
⇒ The two consecutive numbers are 5 and 6.
Hence, option (b).
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