The total number of 4 -digit numbers in which the digits are in descending order, is

Step-by-step solution

Total number of arrangements of 10 digits 0,1,2, , 9 bytaking 4 at atime = ¹⁰ C ₄ 4 ! We observe that in every arrangement of 4 selected digits there is just one arrangement in which the digits are in descending order. Required number of 4 -digit numbers. = ¹⁰ C ₄ 4 ! 4 ! = ¹⁰ C ₄