During multiplication why do you carry numbers?

Answer 1

It's because of the functions of the different columns, or positions in a number. Remember, we can express extremely large numbers, using only nine symbols. The columns mean something. The first column to the left of the decimal is the "units" column. For standard arithmatic in base ten, only the symbols 0 through 9 can go in this or any column. Start with the number 9, and add 1 to it. You now have 10, obviously. You no longer have anything in the "units" column, and you have 1 in the "tens" column. The number 23 has 3 "units", or "ones", and 2 "tens". If you add 7 to it, you see that 7 plus 3 equals 10. The number 10 can't all go in the "units" column. The one has to be added to the "tens" column, because that's what it is-- a "ten". It is this very same idea that comes into play when doing a multiplication.