from gmatprep

d77 wrote:If k is a positive integer and the tens digit of k+5 is 4, what is the tens digit of k
1. k>35
2.the unit sigit of k is greater then 5
why is
2

1) is not sufficient, because the k can be 37 or 42, which does not provide a unique answer.

Whereas:
2) consider the followings:
If the unit digit is less then 5,
--> k's tens digit is 4
if the unit digit is more than 5,
--> k's tens digit is 3

Therefore condition 2) is sufficient, because it restricts the tens digit to be 3 only.