Multiplying a 4-digit number by 137, then
                  by 73; subtract 1200

1. Choose a 4-digit number (one whose numbers are all the same).
2. Multiply by 137 and multiply the product by 73.
3. The second product is an 8-digit number: the original number and a repeat of the digits.
4. Subtract 1200.

   Example:

1. If the first number is 6241:
2. The answer to the two multiplications is 62416241
3. Subtract 1200: 62416241 - 1200 = 62415041
4. So 6241 x 137 x 73 = 62,415,041.

   See the pattern?

1. If the first number is 7834:
2. The answer to the two multiplications is 78347834
3. Subtract 1200: 78347834 - 1200 = 78346634
4. So 7834 x 137 x 73 = 78,346,634.

You can expand this exercise by changing the final step to another calculation: add or subtract a number that is easy to handle. In this way you can create many new exercises.