if x is a sum of all even integers on the interval 13 . . . 55 and y is their number , what is the gcd ( x , y ) ?
"x = 14 + 16 + . . . + 54 = ( largest + smallest ) / 2 * ( # of terms ) = ( 14 + 54 ) / 2 * 21 = 34 * 21 . gcd of 21 and 34 * 21 is 21 answer : b ."
multiply(add(subtract(13, const_10), const_2), add(subtract(13, const_10), const_2))