if x is a sum of all even integers on the interval 13 . . . 65 and y is their number , what is the gcd ( x , y ) ?
"x = 14 + 16 + . . . + 64 = ( largest + smallest ) / 2 * ( # of terms ) = ( 14 + 64 ) / 2 * 26 = 39 * 26 . gcd of 26 and 39 * 26 is 26 . answer : c ."
multiply(add(subtract(13, const_10), const_2), add(subtract(13, const_10), const_2))