Ans – 1 out of 9 digit choose any 4 digit with this there is only one order to arrange in descending order
so 9C4
Ans-2 This is IODB(Identical objects distinct boxes) templete so (4-1+9)C9 = 12C9 = 220
u can choose 1111, 1112, 1122, 1123…...
Ans -3 same as previous one think ans is 220