# Tag: General Knowledge

## Cool Math Tricks

I find it fascinating when I can learn a new trick to help with mathematical problems. So as you can imagine, I thoroughly enjoyed this article!

Cool Mental Math Tricks

The fantastic 11 rule
There is a great likelihood that many people know the 10 rule. That is, when you multiply a number by 10, you add a 0 at the end of the number. However, the 11 rule may be unknown to many. It is so easy to comprehend.
– As you multiply any two digit number by 11
– Let us take 36 for this example (3-6) and notice the gap in between them.
– Then, sum up the two digits, 3 and 6 together
– Put the result, 9 in the gap in between.
– That is simply done 39 x 11=3 96
However, there is one tricky thing that you should remember, if the result after you have added the two digits is more than9, put only the digit representing the “ones” in the gap. For example:
74×11…7_4….4 +7=11…
Put the 1 in the gap, and add 1 to the 7 to get 8, therefore, the answer to 74 x 11 = 814
How to multiply by 999, 99 or 9
Multiplying a number by 9 is just like multiplying it by 10-1.
As such, multiplying 9 × 9 is9 (10-1) whose result is 90 -9 = 81
Another example:
9 × 68… = 68 10-1)
= 680 – 68
= 612
To multiply a number by 99 is the same as by (100-1)
47 multiplied by 99….47 (100-1)
=4700-47…=4653
Multiplying a number by 1000 means the same as multiplying the same by (1000-1)
Therefore, 55 multiplied by 1000 is the same as…..55(1000-1)
=55000-55
=54945
How to squ9are two digit numbers
Take for example that you want to square 48. The first step is squaring each of the digits to get the partial results.
4 × 4 16 and 8 × 8 = 64. Then put the two digits together, 1664.
From there, you should multiply the digits of the number that you want to square….4 × 8=32
Double the resulting product to get 64