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How many 4 digit numbers have 6 as their second digit?
There are 9 digits that can be the first digit (1-9); for each of these there is 1 digit that can be the second digit (6); for each of these there are 10 digits that can be the third digit (0-9); for each of these there are 10 digits that can be the fourth digit (0-9). → number of numbers is 9 × 1 × 10 × 10 = 900 such numbers.
How many two digit numbers are there?
There are 90 two-digit numbers... starting with 10 and ending with 99.
How many 4 digit numbers are palindromes?
There are 90 palindromes with 4 digits.The first digit can be any digit from the set {1,2,3,4,5,6,7,8,9}.With each choice of the first digit, the second can be any digit from the set {0,1,2,3,4,5,6,7,8,9}.That makes 9*10 = 90 permutations for the first two digits. These determine the palindrome since the third and fourth digits are the same as the second and first, respectively.
How many three digit counting numbers are not multiples of 10?
There are 9*10*9 = 810 such numbers.
How many 3 digit numbers can be created if no digit can be repeated?
720 (10*9*8)
