In this post, we are going to learn a very simple strategy for multiplying by 2, 4, and 8.
Strategy for Multiplying a Number by 2:
Multiplying by two is really easy, right? We just have to add the number to itself and we’ll get the answer.
For example:
2 x 48 = 48 + 48 = 96
We’ve doubled 48, and we end up with 96.
Strategy for Multiplying a Number by 4:
We know that 4 = 2 x 2, so in order to multiply by the number 4, we can multiply by two twice. (This is the same as doubling the number 2 times.)
For example:
13 x 4
We can write the 4 as 2 x 2, by doing this we have 13 x 2 x 2.
Let’s start doubling: 13 x 2 = 26
Now, we have to double it again: 26 x 2 = 52
What we did was 13 x 4 = 52
Strategy for Multiplying a Number by 8:
The number 8 can be written as 8 = 2 x 2 x 2, so that means in order to multiply by 8, we can multiply by 2 three times. (This is the same as doubling the number 3 times.)
For example: 13 x 8
By writing 8 = 2 x 2 x 2, we actually have 13 x 2 x 2 x 2
Let’s start doubling: 13 x 2 = 26
And continue: 26 x 2 = 52
And let’s double for the last time: 53 x 2 = 104
What we essentially have done is 13 x 8 = 104
If you want to practice this strategy with more examples, try Smartick for free.
Learn More:
- Adding Strategy for Numbers That Are One or Two Values Apart
- Mental Math: Multiplying by 25 and 75
- How to Multiply by a One-Digit Number
- Mental Math: Multiplying by 11
- Multiplication Tables and Tricks to Learn Them
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