- Each digit of the top number, is multiplied in turn by the two digits of the bottom number.
- Fist we multiply the top number by the units digit of the bottom number.
- Then we multiply the top number by the tens digit of the bottom number.
- The results of these two stages are then added together to give the final result.
Note
Some teaching methods exclude the insertion of the 0 when multiplying by the tens digit. Instead they just offset the digits of each answer
to ensure the correct columns are added together. The inclusion of the zero is preferred here, as it ensure the columns of each number are aligned properly
and highlights the fact that we are multiplying by tens not units!
To multiply larger numbers.
- If the second number had three digits, we would multiply the top number by each of the three digits in turn and then add the three results.
- When multiplying by the hundreds digit we would put two zeros first, to take account the fact that we would be multiplying by hundreds.
- Long multiplication can be done for any size numbers. We simply multiply the first number by each digit in the second number in turn, then add the
results together, (remembering to write the appropriate number of zeros first, when multiplying by tens, hundreds and thousands etc.).
