If r = 199,999 and s = 991,999, which of the following is the units digit of r^5 + s^4?  Pick
A) 0
B) 1
C) 2
D) 8
E) 9
The exponents of 9 cycle between 9 (odd exponents) and 1 (even exponents).   Then the sum of r^5+s^4 will have the units digit of 9+1= 
<gadget id="calculator">9+1</gadget>
<output>10</output>
10 as a units digit.   The answer is 0.
<result>A</result>
If r = 199,999 and s = 991,999, which of the following is the units digit of r^5 + s^4?