pb_india wrote:

If x and y are positive integers, what is the remainder when 3^(4+4x)+9^y is divided by 10?

(1) x=25

(2) y=1

I can do this with "C" but OA is "B"

As a rule of thumb with remainder type questions, most likely we are only concerned with the unit digit....so check for unit digits for each number.

this is interesting....we know that the 3^x changes its unit digit every 4 times i.e.

3^1=3

3^2=9

3^3=7

3^4=1

3^5=3<---repeats...

so we know that 3^4x will always give 1 as unit digit, but we dont know what 9^y is if y is odd it will be 9, if it is even then it will be 9. In this problem we only need to know y to determine if it divisible by 10.