That's how I think : first consider (1) . Let's set a =5x+1 according to the question. Because a.b .c are Consecutive numbers。 b=5x+2 c=5x+3 Add a.b and c together ,we get N, which is 15x+6 . When N is divided by 5 , the reminder is always 1 . Consider(2) because XYC is a three-digit number ,and X divided by 5 has a reminder of 1. The only possible number of X either 1 or 6 . 123 and 678 both have a reminder of 3 . Hence, both are sufficient (D). -- by 会员 sailing198961 (2012/4/16 5:52:20)
Thanks man! |