How many 3 digit numbers can be formed by using the digits 1 to 9 if no digit is repeated?
How many 3 digit numbers can be formed by using the digits 1 to 9 if no digit is repeated?
1,2,3,4,5,6,7,8,9.
There are 9 digits from 1 to 9.
In the 3 digit number, unit digit can be filled in 9 ways
Ten digit can be filled in 8 ways
Hundredth digit can be filled in 7 ways
Therefore total number of ways = 9 x 8 x 7 = 504 ways.
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find x.
when (i) n = 6, r = 2 (ii) n = 9, r = 5