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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. Mark the two multiplications (which will look like a big X). Show the child that this is like multiplying by 100. Have the child place zeros in the two right columns and place the product to the left. Put it together with unit times two digit (1 by 2) 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. Remind the child of the zero in the right column. 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.

Summary:
Make sure the child already knows the basic multiplication tables. Teach the child how to handle multiples of ten; we see this as zeros on the end of a number. Place column lines on the paper and make sure the digits are properly placed. Multiply the Units column and place the answer in the correct columns. Before multiplying the Units column by the Tens column, discuss the implications. Place a zero (0) in the units column underneath the first answer. Multiply the Units column by the tens column and place the answer to the left side of the zero (it will be underneath the first answer). Have the child add the numbers together. Have the child complete the problem with the bottom tens digit hidden (at first). Remind the child that he/she placed a zero in the right column before multiplying a unit column by a tens column. Reveal the hidden digit and show the child that he/she will be multiplying a unit by a tens digit again. Again, have the child place a zero(0) in the right hand column and answer the units x tens multiplication to the left of the zero. Discuss multiplying the tens by the tens column. Have the child do the addition to finish the problem. This time, instead of writing the tens digit (from the unit x unit product) under the line, write it ABOVE the tens digit column. Have the child do the units times tens multiplication; have the child add the carried number to the product and write the number to the left of the units digit already present. Place a tens digit in the lower factor and have the child cross out any carrying that has already taken place. Have the child treat the tens digit like the other one times two digit work. Have the child finish by doing the addition.