Problem:
Determine what is the greatest common divisor among all the numbers that can be written as the sum of 2002 consecutive odd numbers, all positive and less than 10000 (two odd numbers are said to be consecutive if they differ by 2).
Problem:
Determine what is the greatest common divisor among all the numbers that can be written as the sum of 2002 consecutive odd numbers, all positive and less than 10000 (two odd numbers are said to be consecutive if they differ by 2).
Pick one
Solution:
The answer is (D). Let us call the sum of 2002 consecutive odd numbers starting from .
We note that and have 2001 addends in common and that their difference is therefore equal to
The greatest common divisor among the is therefore 4004.
SECOND SOLUTION.
The sum of the first odd numbers from 1 to is , so the sum of 2002 consecutive odd numbers starting from is so they are all multiples of 4004, and two consecutive ones have GCD 4004 because .