Raju wrote first N natural numbers on a blackboard. Later he erased one number and calculated the average of remaining numbers. It turned out to be . Which number did he erased. Correct answer is '15'. Can you explain this answer?

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Raju wrote first N natural numbers on a blackboard. Later he erased one number and calculated the average of remaining numbers. It turned out to be

. Which number did he erased.

Correct answer is '15'. Can you explain this answer?

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Raju wrote first N natural numbers on a blackboard. Later he erased on...

Denominator contains the number 17, which implies number of terms = 17 k
Since the original average must be around 34 - 36, number of terms must be in the range 67-71

Therefore k = 4

Number of terms = 17 x 4 = 68 (after erasing one number) Therefore number of terms originally = 68 + 1 = 69

Original average = (69 + 1 )/2 = 35

Sum of 69 numbers = 35 x 69 = 2415

The number that was erased = 2415 - 2400 = 15
Answer: 15

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Raju wrote first N natural numbers on a blackboard. Later he erased one number and calculated the average of remaining numbers. It turned out to be . Which number did he erased. Correct answer is '15'. Can you explain this answer?

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