Multiply by EightMultiplying by eight is done similar to multiplying by nine except we now double the result after the subtraction and subtract 2 from the left hand digit of the multiplicand.

The Rules For Multiplying By Eight

  1. First Step: subtract from 10 and double.
  2. Middle Steps: subtract from 9 and double what you get, then add the neighbor.
  3. Last Step: subtract two from the left-hand figure of the multiplicand.

An Example - Multiplying 1965 by 8


We will look at the example 1965 x 8.

Again I will setup the expression as before when we were multiplying by nine.
Multiplying by Eight Example 1 Setup

Step 1
For the first step we subtract 5 from 10, giving us 5 and we double it to 10.
Multiplying by Eight Example 1 Step 1
We write down the 0 and carry the 1.

Step 2
Next we subtract 6 from 9, giving us 3, which doubled is 6. We add the neighbor, 5, to give 11 to which we add the carry from the previous step for a total of 12.
Multiplying by Eight Example 1 Step 2
We write down the 2 and carry the 1.

Step 3
Next we subtract 9 from 9 which is zero, doubled is still zero,  adding the neighbor we have 6 then we add the carry for a total of 7.
Multiplying by Eight Example 1 Step 3
We write down the 7.

Step 4
Now we subtract 1 from 8 which is 8, doubling that we get 16. Adding the neighbor, 9, we now have 25.
Multiplying by Eight Example 1 Step 4
We write down the 5 and carry the 2.

Last Step
For the last step we subtract 2 from the neighbor, 1, which is minus 1 then we add the carry, which was 2 giving us a total of 1.
Multiplying by Eight Example 1 Last Step
We write down the 1 giving us our final answer of 15270.

These rules will work for all numbers, however when multiplying a single digit number by 8 you would simply omit rule 2 and only use rules 1 and 3.

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