If you were using the example above, you might say, “We’re almost done. You did seven plus five equals twelve. Good. Four plus three equals seven. Correct. Notice that the four and the three are in the tens position, so you are really adding forty and thirty. "
Simply put: Anytime you multiply by a number with zeros on the end (like 120 x 160), you add the number of zeros to the end of the product. 120 x 160 becomes: 12 * 16 = 192 Place the two zeros on the end (One from 120 and another from 160) = 19,200 Start with a one digit times two digit multiplication problem
Remind the child that the units column has already been multiplied. Tell the child that when you multiply the units column by the tens column it’s like multiplying something with a zero on the end.
Do not continue until the child can manage any problem of this type (1 x 2)! Continue with a two digit times two digit (2 by 2) multiplication problem. Most children have no idea why their teacher skips a space on the second line of “conventional” long multiplication.
Have the child compare this to carrying in addition.
The child should become proficient at this before proceeding. Complete the process of (2 by 2) multiplication.
This would be a good time to tell the child that the zero in the right hand column is not necessary, but it won’t hurt if they leave it.
