0, 1, 2, 3 and 4
6
You need to regroup when you add the numbers together and they add up to a number that is ten or more. For example: 1 164 +518 _____ 682 If it is over ten, take the first digit of the number and put it above the next number. Then, add that number onto the sum of the other digits underneath it.
24680
5040
Regrouping in subtraction means that if you can't subtract because the digit on the bottom has a greater value than the digit on the top (such as 3-6), you have to "regroup" and subtract on from the top digit to the left of the digits your working with and then add a ten to the top digit your working with. Finally, you subtract. (645-9=630+15-9) Hope that makes sense!
15
only 2
No. It depends on how good you are at arithmetic.
460
because 1 is toobig
2
4
6 times
It is possible to create a 3-digit number, without repeated digits so the probability is 1.
6
by one by one
24680