1。 DS. x+y is an integer. if y an integer?
(1) x-y is an integer.
(2)x+2y is an integer.
2。n is a two-digit number. if the ten digit of n less than 3?
(1) the unit digit number is 7 more than the ten digit number.
(2) n is twice as the sum of its unit digit number and ten digit number 3。a car takes x gallon per mile on high way and y gallon per mile in city lanes. given that it uses 6 gallons, and travel 170 miles. what is x? 4. 给了一个图， A /\ /\ /\ /\ /\ /\ /\ C A 是起点，c是最后一行的第3个 问，如果从a出发到c,能有多少probability? rc: 一篇关于恐龙绝种的文章 | 
