9
30,25,15,20, or 10.
10 You can only have one choice, the number 4 as the hundred digit and also one choice, the number 5 as the units digit. However, you can have any integer from 0-9 as the hundreds digit. The number of combinations is thus 1 x 10 x 1 = 10.
Three possible combinations: 17+1, 13+5 and 7+11.
If you have 12 possible numbers with multiple combinations then you should start out with making all the possible combinations; you will find theyre 20. Theyre four numbers out of the twleve that can be divisible by three; 3, 6, 9, and 12. There are 7 combinations where the combinations can equal those four numbers. So the odds of getting a sum divisible by three is 7/20.
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.
9
6 ways: 931,913,139,193,391,319
30,25,15,20, or 10.
10 You can only have one choice, the number 4 as the hundred digit and also one choice, the number 5 as the units digit. However, you can have any integer from 0-9 as the hundreds digit. The number of combinations is thus 1 x 10 x 1 = 10.
There are 28706 such combinations. 5456 of these comprise three 2-digit numbers, 19008 comprise two 2-digit numbers and two 1-digit numbers, 4158 comprise one 2-digit number and four 1-digit numbers and 84 comprise six 1-digit numbers.
21
Only three: 12, 13 and 23. Remember that the combinations 12 and 21 are the same.
There are no three-digit numbers that equal 17. In fact, there are no numbers with more or less than two digits that equal 17. In fact, in the whole infinite supply of numbers, there is only one single number that equals 17. That number is . . . . . . . 17 .
21.
Three possible combinations: 17+1, 13+5 and 7+11.
NOT AN ANSWER:More acceptable combinations:1231 3213 2321More unacceptable combinations:1112 2222 3113Thanks.