If each permutation of the digits 1,2,3,4,5,6 are listed in the increasing order of magnitude, then ...
If each permutation of the digits 1,2,3,4,5,6 are listed in the increasing order of magnitude, then 289thterm will be
Answer/Solution
341256
Steps/Work
Explanation :
Let's see how many numbers can be formed with the left most digit as 1
The digit '1' is placed at the 1st position (only 1 way of doing this)
Since one digit is placed at the 1st position,
any of the remaining 5 digits can be placed at 2nd position.
Since one digit is placed at the 1st position and another digit is placed
at the 2nd position, any of the remaining 4 digits can be placed at the
3rd position.
So on ...
1 5 4 3 2 1
i.e., total number of ways = (1)( 5)( 4)( 3)( 2)( 1) = 120
i.e., total count of numbers which can be formed
with the left most digit as 1 = 120
Similarly, total count of numbers which can be formed
with the left most digit as 2 = 120
Similarly, total count of numbers which can be formed
with the left most digit as 3 = 120
i.e., 240 numbers (=120 + 120) can be formed
(with left most digit as 1) or (with left most digit as 2)
Similarly, 360 numbers (=120 + 120 + 120) can be formed
(with left most digit as 1) or (with left most digit as 2)
or (with left most digit as 3)
Hence, the left most digit of the 249th number = 3
Now, let's find out how many numbers can be formed
with the left most digit as 3 and next digit as 1
The digit '3' is placed at the 1st position (only 1 way of doing this)
The digit '1' is placed at the 2nd position (only 1 way of doing this)
Any of the remaining 4 digits can be placed at 3rd position.
Since 3 digits are placed in the first three positions, any of the remaining 3 digits
can be placed at the 4th position.
Since 4 digits are placed in the first four positions, any of the remaining 2 digits
can be placed at the 5th position.
Since 5 digits are placed in the first five positions, the remaining 1 digit
can be placed at the 6th position.
1 1 4 3 2 1
i.e., total number of ways = (1)(1)(4)(3)(2)(1) = 24
i.e., Total count of numbers which can be formed
(with the left most digit as 3) and (next digit as 1) = 24
Similarly, total count of numbers which can be formed
(with the left most digit as 3) and (next digit as 2) = 24
Hence, 120 + 120 + 24 + 24 = 288 numbers can be formed
(with left most digit as 1) or (with left most digit as 2)
or (with left most digit as 3 and next digit as 1)
or (with left most digit as 3 and next digit as 2)
Hence, the 289th number is the minimum value number which is formed
with the left most digit as 3 and next digit as 4.
i.e., the number is 341256
Answer : D
Let's see how many numbers can be formed with the left most digit as 1
The digit '1' is placed at the 1st position (only 1 way of doing this)
Since one digit is placed at the 1st position,
any of the remaining 5 digits can be placed at 2nd position.
Since one digit is placed at the 1st position and another digit is placed
at the 2nd position, any of the remaining 4 digits can be placed at the
3rd position.
So on ...
1 5 4 3 2 1
i.e., total number of ways = (1)( 5)( 4)( 3)( 2)( 1) = 120
i.e., total count of numbers which can be formed
with the left most digit as 1 = 120
Similarly, total count of numbers which can be formed
with the left most digit as 2 = 120
Similarly, total count of numbers which can be formed
with the left most digit as 3 = 120
i.e., 240 numbers (=120 + 120) can be formed
(with left most digit as 1) or (with left most digit as 2)
Similarly, 360 numbers (=120 + 120 + 120) can be formed
(with left most digit as 1) or (with left most digit as 2)
or (with left most digit as 3)
Hence, the left most digit of the 249th number = 3
Now, let's find out how many numbers can be formed
with the left most digit as 3 and next digit as 1
The digit '3' is placed at the 1st position (only 1 way of doing this)
The digit '1' is placed at the 2nd position (only 1 way of doing this)
Any of the remaining 4 digits can be placed at 3rd position.
Since 3 digits are placed in the first three positions, any of the remaining 3 digits
can be placed at the 4th position.
Since 4 digits are placed in the first four positions, any of the remaining 2 digits
can be placed at the 5th position.
Since 5 digits are placed in the first five positions, the remaining 1 digit
can be placed at the 6th position.
1 1 4 3 2 1
i.e., total number of ways = (1)(1)(4)(3)(2)(1) = 24
i.e., Total count of numbers which can be formed
(with the left most digit as 3) and (next digit as 1) = 24
Similarly, total count of numbers which can be formed
(with the left most digit as 3) and (next digit as 2) = 24
Hence, 120 + 120 + 24 + 24 = 288 numbers can be formed
(with left most digit as 1) or (with left most digit as 2)
or (with left most digit as 3 and next digit as 1)
or (with left most digit as 3 and next digit as 2)
Hence, the 289th number is the minimum value number which is formed
with the left most digit as 3 and next digit as 4.
i.e., the number is 341256
Answer : D