In this lesson, students learn to use the standard algorithm to multiply a four-digit number by a one-digit number when regrouping is required in the tens place, the hundreds place, and the thousands place.
In doing the multiplication problems students are not required to show the results of regrouping as notations at the top of the problem, but only enter their final answer, which is evaluated in its entirety.
In this lesson, students learn how to use the standard algorithm to multiply a two-digit number by a two-digit number.
Students first learn to solve the problem by splitting it into two problems that result with the bottom number (the multiplier) is written in expanded form as a number of tens and a number of ones.
They then multiply the top number (the multiplicand) by the number of ones in the multiplier.
Next they multiply the multiplicand by the number of tens. Earlier, students have learned that multiplying a number by ten means you add a zero to the number to make a two-digit number that represents some number of tens. They use this knowledge to complete the multiplication of tens times the multiplication.
When both multiplications are completed, the two products are added to produce the answer to the original multiplication problem.
Finally, students learn how to complete the same process by combining both multiplications in the same process, which is the standard algorithm for multiplication.