2 How many four digits are formed such that the digits are in decreasing order

ANS:210
0,1,2,3,4,5,6,7,8,9
3C3=1
4C3=4
5C3=10
6C3=20
7C3=35
8C3=56
9C3=84
TOTAL=210
9 years agoHelpfull: Yes(24) No(3)
ans is 10C4
9 years agoHelpfull: Yes(7) No(0)
Decreasing order lowest 3210
Decreasing order highest 9876
Therefore,
In 1st digit---->(3 to 9) =7 numbers
In 2nd digit---->(2 to 8) =7 numbers
In 3rd digit---->(1 to 7) =7 numbers
In 4th digit---->(0 to 6) =7 numbers
Therefore,four digits numbers are formed such that the digits are in decreasing order =(7+7+7+7)=28 (ans.)
9 years agoHelpfull: Yes(4) No(6)
10C4=210
as the numbers are 9,8,7,6,5,4,3,2,1,0
and we have to select any 4 digits out of all 10 digits
9 years agoHelpfull: Yes(4) No(0)
Can you please explain this? @KARTHIKEYANK
9 years agoHelpfull: Yes(2) No(0)
i cant understand, can u plz xplain dis
9 years agoHelpfull: Yes(1) No(0)
lets start with 3_ _ _. You can fill in with digits 0,1,2.
That is 3210
Hence 3C3 = 1
START with 4 = 4_ _ _. (0,1,2,3).
That is 4321,4320,4310,4210
hence 4C3= 4
START with 5, you have (0,1,2,3,4) to fill in the blanks behind 5,
That is 5432,5431,5430,5421,5420,5410,5321,5320,5310,5210
hence 5C3 = 10
Similarly
START with 6, 6C3=20
7... = 7C3 = 35
8...=8C3 = 56
9...= 9C3 = 84
so ans=1+4+10+20+35+56+84=210
9 years agoHelpfull: Yes(1) No(2)
ans -468
7*3c3+6*4c3+5*5c3+4*6c3+3*7c3+2*8c3+1*9c3

solve it -468
9 years agoHelpfull: Yes(0) No(1)
you have done very good job ASD ..keep it up
8 years agoHelpfull: Yes(0) No(0)

2) How many four digits are formed such that the digits are in decreasing order