How to Double a Number
Write out the problem., Add the numbers on the right., Carry any digit greater than 10 to the left., Add the next set of numbers., Repeat until you reach the end of the line., Write the final answer.
Step-by-Step Guide
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Step 1: Write out the problem.
For this method, you'll need to write out the problem as any other addition problem.
Write the number twice, placing a plus sign in between.
Example:
Find the double of
357.
Write the problem as you would write out any other addition problem: 357 + 357 -
Step 2: Add the numbers on the right.
Add the right-hand digits of both written values together.
Essentially, you are simply doubling the right-hand digit.
Example:
For 357 + 357, the number on the right is
7. 7 + 7 = 14 , If the sum of the right-hand digits is 10 or greater, you will need to carry the value in the “tens” place position over to the next set of digits.
Only write the number in the “ones” place position as part of your answer.
Example:
In this problem, 14 is greater than 10, so the you must carry the 1 over to the next place setting.
The 4 will be the right-most digit in your answer. , Add the next set of digits together, moving to the left.
If you carried over a “1” from the previous place setting, you should add that to the two digits, as well.
Example:
For 357 + 357, the next digit to the left is
5.
Since you carried over 1 from the previous place setting, you must also add it to the doubled value of this place setting. 5 + 5 + 1 = 11 , Continue through the rest of the number in the same manner, working from right to left, until you reach the final set of digits on the left-hand side of the total value.
Example:
Since 11 is greater than 10, you will need to carry the extra 1 over to the next place setting.
The right-hand 1 will be the middle digit in your answer.
There is only one place setting left to deal with in this answer.
You will need to add the values of this place setting together along with the 1 you carried over: 3 + 3 + 1 = 7 This 7 will be the left-most digit in your answer. , If you haven't done so already, write the calculated sums from each place position side-by-side.
This answer should be the doubled amount of your original number.
Example:
The left-most digit is
7.
The middle digit is
1.
The right-most digit is
4.
When written together, the answer is '714.
Therefore, the double of 357 is
714. -
Step 3: Carry any digit greater than 10 to the left.
-
Step 4: Add the next set of numbers.
-
Step 5: Repeat until you reach the end of the line.
-
Step 6: Write the final answer.
Detailed Guide
For this method, you'll need to write out the problem as any other addition problem.
Write the number twice, placing a plus sign in between.
Example:
Find the double of
357.
Write the problem as you would write out any other addition problem: 357 + 357
Add the right-hand digits of both written values together.
Essentially, you are simply doubling the right-hand digit.
Example:
For 357 + 357, the number on the right is
7. 7 + 7 = 14 , If the sum of the right-hand digits is 10 or greater, you will need to carry the value in the “tens” place position over to the next set of digits.
Only write the number in the “ones” place position as part of your answer.
Example:
In this problem, 14 is greater than 10, so the you must carry the 1 over to the next place setting.
The 4 will be the right-most digit in your answer. , Add the next set of digits together, moving to the left.
If you carried over a “1” from the previous place setting, you should add that to the two digits, as well.
Example:
For 357 + 357, the next digit to the left is
5.
Since you carried over 1 from the previous place setting, you must also add it to the doubled value of this place setting. 5 + 5 + 1 = 11 , Continue through the rest of the number in the same manner, working from right to left, until you reach the final set of digits on the left-hand side of the total value.
Example:
Since 11 is greater than 10, you will need to carry the extra 1 over to the next place setting.
The right-hand 1 will be the middle digit in your answer.
There is only one place setting left to deal with in this answer.
You will need to add the values of this place setting together along with the 1 you carried over: 3 + 3 + 1 = 7 This 7 will be the left-most digit in your answer. , If you haven't done so already, write the calculated sums from each place position side-by-side.
This answer should be the doubled amount of your original number.
Example:
The left-most digit is
7.
The middle digit is
1.
The right-most digit is
4.
When written together, the answer is '714.
Therefore, the double of 357 is
714.
About the Author
Cheryl Walker
Writer and educator with a focus on practical DIY projects knowledge.
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