Let A be the set of four-digit numbers A1,A2,A3,A4 where A1>A2>A3>A4,Then how many of A are possible?
There are 210 such integers, which begin with 3210 , 4210 , 4310 , 4320 , 4321 , 5210 , 5310 , 5320 , 5321...........and end with 9865 , 9870 , 9871 , 9872 , 9873 , 9874 , 9875 , 9876 , Total = 210
