Vshal wrote:
What is the units digit of 15^x + 22^y , where x and y are natural numbers ?
(1) x = 6
(2) y = 18
FYI, to my knowledge the GMAT does not use the term natural numbers. The GMAT will instead say "where x and y are positive integers"
(1) x=6 notice that any power of 5 gives us a units digit = 5, so this statement provides no useful info NS
(2) y = 18. The units digit for powers of 2 follows the following pattern: 2,4,8,6,2,4,8,6. Knowing y tells us which position in the sequence to take for the units digit of 22^y. The units digit of 15^x will always be 5 therefore 2 is suff. B