using digits 1-9 only once, multiply a 3 digit by a 2 digit number and get a 4 digit result

12*345=4140?

looks ok to me.

the answer would have to be 6789 or some order of those digits if you used the others in the question. digits 1-9 used only once, no zeroes.

The digits can be used in any order. We have gotten 8 out of 9 digits in one problem 456x13=5928 (2 fives and no 7). Will keep trying.

To find a 3-digit number multiplied by a 2-digit number that results in a 4-digit number, using digits 1-9 only once, you can follow these steps:

1. Start by listing all possible combinations of 3-digit numbers using 3 out of the given 9 digits. There are a total of 9P3 = 504 possible combinations. For example, one combination could be 123.

2. Next, list all possible combinations of 2-digit numbers using the remaining 6 digits. There are a total of 6P2 = 30 possible combinations. For example, one combination could be 45.

3. Multiply each 3-digit number by each 2-digit number and check if the product is a 4-digit number. For the example combination, 123 multiplied by 45 results in 5535, which is not a 4-digit number.

4. Repeat this process for all possible combinations until you find a multiplication that gives a 4-digit result.

Keep in mind that this method may require some trial and error, as not all combinations will result in a 4-digit number.