1. It is obviously that with knowledge of n and m we will have one integer and one reminder. So, C works good. But what about A and B? Maybe GMAT want to trick us with C-Trap?
2. take a look on m. It is definitely clear that at m=2 and m=3 we will have different reminders. So the second condition is necessary.
3. What about the first condition? First of all we have 4*n instead of n and it is a small prompt to dig deeper.
4. What do the reminder mean here? when we divide an integer by 10 we will get a reminder that is equal to the unit digit of the integer. So, the unit digit.....and power......
5. Let write unit digits of some powers of 3:
6. What do we see here? period 4 !!! the unit digit is defined by the reminder of the power divided by 4. Actually reminder of 4n+2 is always 2. So, we have found a trap! the answer is B
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