Quick Eight Times (I)

By now we have discovered tricks to find out twice, thrice, four times, five times, six times, seven times, nine times and ten times of any number quickly. The only multiplication that remains to be discovered is of eight times. If we find out a short cut for answering eight times we will be in a position to manage all sorts of multiplications quickly.

Our aim so far has been to keep calculations very easy and minimal. All our methods discovered so far require doubling, halving of a single digit, which is then added to or subtracted from the neighboring digit, as per the requirement. In finding eight times of any number we will adhere to the same principle.

Let us say, we want to know eight times 18. As you can see there are two ways to manage this task. One way would be to find five times of 18, first and then adding three times 18 to it. If we accept this approach we will have to find out three times of 18 or whatever number we have, making our calculations slightly difficult as well as time consuming.

Another approach would be to find ten times of 18, first. From this product we will then be subtracting double/twice of 18. This approach will be much easier than the earlier one. The reason is finding ten times of any number requires adding just a zero to the right end of that number. We already have a simple way to get twice of any number. If you want to refresh your memory on this please read through the article Quick Two Times.

Finally, we need to manage a simple subtraction, which is not a difficult task for us.

Using the second approach let us calculate eight times 18: Step I: Ten times 18 is 180. Step II: Two times 18 is 36. Step III: Subtract 36 from 180. 180 - 36 = 144

Thus, 8 times 18 is 144. Using your normal approach, check out the answer and you know it is indeed the right answer.

As usual, we will now closely observe which digit of 'twice eight' gets subtracted from which digit of 'ten times'. For this purpose we write down the minuend and the subtrahend one below the other, as shown below: .

This figure reveals a simple rule: Subtract twice the digit from its right neighbor!

Though the rule is simple we have to decide on two things.

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