Explain that with standard algorithm multiplication you start by putting the numbers one under the other. You put the larger number on top. The T, H, T, O above the chart refer to the thousands, hundreds, tens, and ones. Show that above each column there is a regrouping box. In these boxes you can write down regrouped numbers and add them up with the other outcomes later. Explain that with standard algorithm multiplication with a tens number you can write down a 0 in the ones place, because all multiplications with this number make 0. Briefly show that this is true for the problems 0 x 3 and 0 x 6. Now multiply the lower number from the tens (T) column and the higher number from the ones (O) column. Write down the 5 under the line in the tens (T) column and the 1 in the regrouping box from the hundreds (H). Next you multiply the lower number from the tens (T) column with the higher number from the tens (T) column (5 x 6 = 30). Emphasize that you add the 1 from the regrouping box to your answer (30 + 31 = 31). Write this answer under the line in the hundreds and thousands columns. Practice two problems together with the students that must be solved using the standard algorithm. Students may use a sheet of scrap paper. The students solve the next three problems on their own.
Check whether the students can multiply using the standard algorithm with a tens number and a number to 100, by asking the following question:
- What steps do you take to solve the problem 80 × 54 using the standard algorithm?