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Study Stuff for MCA Examinations - NIMCET
Study Stuff for MCA Examinations - NIMCET
Previous Year Question (PYQs)
A teacher gave a student the task of adding ‘N’ natural numbers starting from 1. After a while, the student reported his result as 700. The teacher replied that the result was wrong. The student realized he had added one number twice. Find the sum of digits of the number which the student had added twice.
Solution
Sum 1 to N = N(N+1)/2.
A nearby perfect sum around 700 is 702 because 37×38/2 = 703.
If actual should be 703 and student got 700 → he added a number 3 twice less? No.
Student's mistake makes his sum 700 = correct sum + repeated number.
Try 704 (for N = 37): 703 + x = 700 (impossible)
Try N = 36: sum = 666 → 666 + x = 700 → x = 34
Sum of digits of 34 = 7
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