Finger Math: 9X Rule

To multiply by 9,try this:

(1) Spread your two hands out and place them on a desk or table in front of you.
(2) To multiply by 3, fold down the 3rd finger from the left. To multiply by 4, it would be the 4th finger and so on.
(3) the answer is 27 ... READ it from the two fingers on the left of the folded down finger and the 7 fingers on the right of it.

This works for anything up to 9x10!

Multiply Up to 20X20 In Your Head

In just FIVE minutes you should learn to quickly multiply up to 20x20 in your head.  With this trick, you will be able to multiply any two numbers from 11 to 19 in your head quickly, without the use of a calculator.

I will assume that you know your multiplication table reasonably well up to 10x10.

Try this:

• Take 15 x 13 for an example.
• Always place the larger number of the two on top in your mind.
• Then draw the shape of Africa mentally so it covers the 15 and the 3 from the 13 below. Those covered numbers are all you need.
• First add 15 + 3 = 18
• Add a zero behind it (multiply by 10) to get 180.
• Multiply the covered lower 3 x the single digit above it the "5" (3x5= 15)
• Add 180 + 15 = 195.

Product of Numbers close to 100:

Lets take you have to multiply 91 and 95 . First take their difference from 100. ie 100-91=9and 100-95=5 . Now reduce this difference from the other number .ie 91-5 or 95-9 ==86 . This is the first 2 digits of the result . Now for the last 2 digits just multiply the differences ,ie, 9*5=45.

So the result is  91*95=8645.

How many squares are there?

How many squares are there?

Usually, we get some puzzle like this. I would like to share trick that can solve this kind of puzzle so easily.
In perfect 4*4 square, to find out the number of squares,
4^2=16
3^2=9
2^2=4
1^1=1
Total number of squares would be 16+9+4+1=30.

Same ways, the answer for squares in 7*7 is,
49+36+25+16+9+4+1=140.

This works perfectly fine when there are same number of rows and columns.

But what if, there are different numbers of rows and columns into it.
For Example,

if there is a rectangle, which has 5 rows and 4 columns and still we have to find the total number of square in it. It would not be possible with the above method.

For this, there is a simple trick,

Rows- 5 Column-4

STEP 1) Multiply the number of rows into number of column
In this case 5*4 = 20
STEP 2) Reduce 1 from number of rows and column
In this case 4*3 = 12
STEP 3) Follow STEP 2 until either of row or column count comes to 1.
In this case 3*2 = 6, 2*1 =2

As we see above the column count has come to 1 so reducing it to zero wont make any sense. 

Total = 20 + 12 + 6 + 2 = 40

Square a 2 Digit Number Ending in 5

For this example we will use 25

• Take the "tens" part of the number (the 2 and add 1)=3
• Multiply the original "tens" part of the number by the new number (2x3)
• Take the result (2x3=6) and put 25 behind it. Result the answer 625.

Try a few more 75 squared ... = 7x8=56 ... put 25 behind it is 5625.
55 squared = 5x6=30 ... put 25 behind it ... is 3025. Another easy one! Practice it on paper first!