$$8+7+6+5+4+3+2+1=36$$. 
How many two-digit numbers are there where the ones digit is greater than the tens digit? (2008 Math Kangaroo Problem, Level 3-4, Question \#21) 

(1) $$26$$ 
(2) $$18$$ 
(3) $$9$$ 
(4) $$30$$ 
(5) $$36$$ 