What is 3 4 doubled

Double numbers

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To double a number we have two ways to do it in our head:

Double as "add the number to itself"

We add the number to itself, adding the individual digits together.

Example:

 

Double as "Multiply the number by 2"

Here we multiply the number by, which is equivalent to adding the number to itself (as shown earlier).

Example:

Calculation:

Every single digit of the number is multiplied with. So

No matter which variant we choose, the end result is the same and the calculations are very similar.

Carries forward when doubling

We have to make sure that adding or multiplying in places can also lead to carryovers (to the next highest place).

An example is shown below:

Double the number "746" by adding

The Carry-overs are marked in bold:

  
 
= 
 
 

Double the number "479" by means of multiplication

We multiply each digit by, it results:

 
times :

Calculation in the head

If we double the number in our head, it makes sense to split the number down in places (as a sum) and then to double the individual summands.

Example: doubling the number

Now we double each summand:

Then we add the doubled summands together and get the result: