There are 5,461,512 such combinations.
64
I am assuming you mean 3-number combinations rather than 3 digit combinations. Otherwise you have to treat 21 as a 2-digit number and equate it to 1-and-2. There are 21C3 combinations = 21*20*19/(3*2*1) = 7980 combinations.
6 of them.
44
There are 5,461,512 such combinations.
64
Number of 7 digit combinations out of the 10 one-digit numbers = 120.
I am assuming you mean 3-number combinations rather than 3 digit combinations. Otherwise you have to treat 21 as a 2-digit number and equate it to 1-and-2. There are 21C3 combinations = 21*20*19/(3*2*1) = 7980 combinations.
6 of them.
44
The answer will depend on how many digits there are in each of the 30 numbers. If the 30 numbers are all 6-digit numbers then the answer is NONE! If the 30 numbers are the first 30 counting numbers then there are 126 combinations of five 1-digit numbers, 1764 combinations of three 1-digit numbers and one 2-digit number, and 1710 combinations of one 1-digit number and two 2-digit numbers. That makes a total of 3600 5-digit combinations.
How many four digit combinations can be made from the number nine? Example, 1+1+2+5=9.
the answer is = first 2-digit number by using 48= 28,82 and in 3 digit is=282,228,822,822
There are 126 different 5 digit combinations. Note that the combination 12345 is the same as the combination 45312.
There are twelve possible solutions using the rule you stated.
There are 15180 combinations.