Doubling large numbers may seem difficult at first, but it gets easier as you practice. There are various methods you can use to double a number. Learn them all, then use the one that is easiest for you the next time you face a doubling problem.
Steps
Method 1 of 3: Addition
Step 1. Write down the calculation that represents the problem
With this method, you will have to express the problem as any addition problem. Write the number twice and put the '+' sign between the two numbers.
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Example: Calculate double 357.
Write the problem as you would for any problem involving an addition: 357 + 357
Step 2. Add the rightmost digits
Add the digits to the right of the two values you wrote. Essentially, you are simply doubling the last digit.
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Example: In 357 + 357, the rightmost digit is
Step 7
7 + 7 = 14
Step 3. If the sum exceeds 10, write the carry-over on the figure immediately to the left
If the total of the right-most digits is 10 or more, you will need to write the carry over in the “tens” column on the next set of digits. In the result, write only the "units" of the number obtained.
Example: In this problem, 14 is greater than 10, so you need to carry 1 on the next column. The 4 will be the rightmost number of the result
Step 4. Add the second column
Add the next two digits, moving left. If you have a carry of “1” from the previous column, you need to add it to the two digits.
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Example: For 357 + 357, the next digit on the left is the
Step 5
- Since you have a carry of 1 from the previous column, you must also add this to the doubled value of this column.
- 5 + 5 + 1 = 11
Double a Number Step 5 Step 5. Repeat until you finish the calculation
Continue with the other columns in the same way, working from left to right, until you reach the last digits on the left and find their total.
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Example: Since 11 is greater than 10, you will have to write a carry of 1 on the next column. The 1 on the right will be the middle digit of the value you are looking for.
- In this example, there is only one other column to calculate. You will need to add the digits of this column and the carry-over of 1 that derives from the previous one: 3 + 3 + 1 = 7
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The
Step 7. will be the leftmost digit of the result.
Double a Number Step 6 Step 6. Write the final result
If you haven't already, write all the digits you got next to each other. This result, if correct, is double the original number.
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Example: The leftmost digit is 7. The middle digit is 1. The rightmost digit is 4. Writing them down, we get '714.
So, the double of 357 is 714
Method 2 of 3: Double by Columns
Double a Number Step 7 Step 1. Double the leftmost digit
Look at the first digit of the number (the leftmost digit, which represents the highest place value). Mentally double that figure and write down the result. This number will be the first or first two digits of the final result.
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Example: Find double 872.
- The leftmost digit is 8.
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Double 8 is
Step 16..
Double a Number Step 8 Step 2. Look at the second digit
If the second digit is equal to or greater than 5, you will need to add 1 to the number found in the previous step.
- If the second digit is less than 5, you don't need to add anything to the previous result.
- Doubling any number between 5 and 9 will result in a two-digit number, which will require this step. Doubling a digit between 0 and 4 will result in a single digit number.
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Example: The second digit of 872 is 7. Since 7 is greater than 5, you will need to add 1 to the sum obtained in the previous step.
- 16 + 1 = 17
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This means that the first two digits of the final result will be
Step 17..
Double a Number Step 9 Step 3. Double the second digit
Go back to the second digit and double it. This value will be the next digit of the final result.
- If the value found in this step consists of two digits, ignore the one that corresponds to the tens and note only the one that indicates the units.
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Example: The second digit of 872 is 7.
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Double 7 is
Step 14..
- Ignore the tens (1) and write the number corresponding to the units (4) in the result.
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This
Step 4. it will be in the middle of the number you are looking for.
Double a Number Step 10 Step 4. Repeat moving to the right
Continue in the same way with the remaining digits, working from left to right, until you have doubled the last digit, the one that indicates the "units" of the number.
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Example: In this problem, there is only one number left to double.
- The last digit of 872 is 2. Since 2 is less than 5, you won't have to add anything to the middle value you get.
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The double of 2 is
Step 4.. This will be the last digit of the final result.
Double a Number Step 11 Step 5. Write the result
Write in order all the values you have obtained. This will be the end result.
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Example: The first part of the result is 17. The middle digit is 4. The final digit is 4. Writing them below, you get 1744.
So, the double of 872 is 1744
Method 3 of 3: Double Partitions
Double a Number Step 12 Step 1. Break down the numbers
Break down or break down numbers into units, tens, hundreds, thousands, and so on. Write them in extended form.
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Example: Calculate double 453.
By breaking down the number, you get: 453 = 400 + 50 + 3
Double a Number Step 13 Step 2. Double each part
Look at the numbers you get and double them all separately.
- To double the numbers from tens upwards, double the non-zero digit, then follow the number of zeros already present to the value obtained.
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Example: You will need to double 400, 50 and 3 separately.
- Since the double of 4 is 8, the double of 400 is 800.
- Since the double of 5 is 10, the double of 50 is 100.
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Double 3 is
Step 6..
Double a Number Step 14 Step 3. Add all the results
Add the doubled values to get the result written in standard form.
Example: 800 + 100 + 6 = 906
Double a Number Step 15 Step 4. Write the result
If the calculations are correct, the number obtained by adding the doubled values will be double the starting number and will constitute the final result.
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