If r = 199,999 and s = 991,999, which of the following is the units digit of r^3 + s^3?
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^3+s^3 will have the units digit of 9+9= 
<gadget id="calculator">9+9</gadget>
<output>18</output>
18 as a units digit.   The answer is 8.
<result>D</result>
If r = 199,999 and s = 991,999, which of the following is the units digit of r^3 + s^3?