A four digit number is called a doublet if any of its digit is the same as only one neighbour. For example, 1221 is a doublet but 1222 is not. Number of such doublets are

A four digit number is called a doublet if any of its digit is the same as only one neighbour. For example,1221 is a doublet but 122 is not. Number of such doublets are

How many four digit numbers can be formed with the digits 3,5,7 and 9 only ?

How many four digit numbers are there with distinct digits?

Number of four digit numbers in which at least one digit occurs more than once, is :

A two digit number is 4 times the sum of its digits and the unit digit is 3 more than the tens digit . the number is :

Let ' m ' denotes the number of four digit numbers such that the left most digit is odd, the second digit is even and all four digits are different and ' n ' denotes the number of four digit numbers such that left most digit is even, second digit is odd and all four digit are different. If m=nk, then k equals :

A three digit number abc is 459 more than the sum of its digits.What is the sum of the 2digit number ab and one digit number a?

Successor of a one digit number is always a one digit number.

Number of 6 digit numbers that can be formed using digit 2 two times and the digit 5 four times is