270*3 реши столбиком

                        2 7 0
                      * 3
                    _______
                      2 7 0   (3 * 0 = 0)
             +    8 1 0   (3 * 7 = 21, write 1 and carry 2)
          +   8 1 0    (3 * 7 = 21, write 1 and carry 2)
       _______________
        8 1 0  0

Therefore, 270 * 3 = 810.