how many four digits numbers are formed such that the digits are in decreasing order
Choices
A) 170
B) 180
C) 190
D) 200
E) 210
START with 3 = 3_ _ _. You can fill in with digits 0,1,2. Hence 3C3 = 1   START with 4 = 4_ _ _. (0,1,2,3). hence 4C3= 4   START with 5, you have (0,1,2,3,4) to fill in the blanks behind 5, hence 5C3 = 10   START with 6, 6C3=20   7... = 7C3 = 35   8...=8C3 = 56   9...= 9C3 = 84   so ans=1+4+10+20+35+56+84= 
<gadget id="calculator">1+4+10+20+35+56+84</gadget>
<output>210</output>
210   ANSW210R:210
<result>E</result>
how many four digits numbers are formed such that the digits are in decreasing order