If x is a sum of all even integers on the interval 13...63 and y is their number, what is the GCD (x, y)?
Choose the correct choice from the following answers: A) 1 B) 13 C) 26 D) 25 E) 1014
x = 14 + 16 + ... + 62 = (largest + smallest)/2 *(# of terms) = (14 + 62)/2*25 = 38*25.   GCD of 25 and 39*25 is 25.   Answer: 25.
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If x is a sum of all even integers on the interval 13...63 and y is their number, what is the GCD (x, y)?