If r = 199,999 and s = 991,999, which of the following is the units digit of r^4 + 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^4+s^3 will have the units digit of 1+9= 
<gadget id="calculator">1+9</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^4 + s^3?