if x is a sum of all even integers on the interval 23 . . . 65 and y is their number , what is the gcd ( x , y ) ?
"x = 24 + 16 + . . . + 64 = ( largest + smallest ) / 2 * ( # of terms ) = ( 24 + 64 ) / 2 * 21 = 44 * 16 . gcd of 21 and 44 * 21 is 21 . answer : b ."
multiply(add(subtract(23, const_10), const_2), add(subtract(23, const_10), const_2))