Speed-Multiplication by 11 (without carries)

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Speed-Multiplication by 11
with carrying

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In this case, some of the digits next to each other are going to add to more than nine. Each time that happens, you write the ones digit in the answer column below the digit you are working on, but you mentally (DO NOT WRITE IT DOWN!) carry a one to the next addition. The movie clip will illustrate the steps.

As you read the steps, click the start button to illustrate them.

Step 1: as usual, pretend there are two invisible zeroes, one in front, and one behind the number to be multiplied.	Step 2: as usual, add the last zero to the digit in the ones column, and write the answer below the ones column.	Step 3: Add the digits in the ones and tens columns and write the final digit of the answer below the tens column. Mentally (DO NOT WRITE IT DOWN!) carry the first digit (the 1) along to the next step.




Step 4: Add the digits in the tens and hundreds column, plus the carried 1, and write the final digit of the answer below the hundreds column. Mentally (DO NOT WRITE IT DOWN!) carry the first digit (the 1) along to the next step.	Step 5: Add the digit in the hundreds column to the imaginary 0 in the thousands column, plus the carried 1, and write the answer below the thousands column.	Step 6: There is no step 6 in this lesson, either.

This method works with any number, no matter how long or short, times 11. The next page will be about why it works and how you can use it to learn how to do other numbers. In the meantime practice it with a few long, random numbers times 11.

next lesson - speed multiplication by 12

Want to learn how to mentally multiply any whole number by a number made up of many repeating ones, like 111, or 111,111? If you understand what you've learned here, it's easy to use it to learn largers numbers.

Learn how at my Squidoo Lens at: http://www.squidoo.com/multiplication

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