How many 6-digit numbers can be formed using the digits 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , and 9 if the first digit can not be 0 ? Repeated digits are allowed .
How many 3 digit numbers can be formed using the digits 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 if repetitions of digits are allowed ?