if the average ( arithmetic mean ) of 7 consecutive integers is 20 , then the product of the greatest and least integer is	Choose the correct choice:  A) 343  B) 393  C) 363  D) 391  E) 409

Rationale: n = smallest number n + 6 = largest number ( n + n + 6 ) / 2 = 20 = > ( 2 n + 6 ) / 2 = 20 = > n + 3 = 20 = > n = 17 so product of n and n + 6 = ( 17 ) ( 23 ) = 391 answer - d
Answer: D