How many positive integers less than 2017 are divisible by 2 but not by 3?
2017/2 = 1008.5
1008 are divisable by 2
2,4,6,8,10,12, ... as you can see, every third one is also divisable by 3
2/3*1008 = 672
So 672 of them are not divisable by 3
Here is another way:
2017/2 =1008 divisible by 2 - 2017/6 =336 divisible by 6.
1008 - 336 =672 - divisible by 2 but not by 3.
+422 
