1. Multiplication of any two numbers, lies between 11 and 1913*19 = (13+9)*10 + (3*9) = 220 + 27 = 247 Example : 18*14 = (18+4)*10 + (8*4) = 220 + 32 = 252 
2. EXCLUSIVE DIVISION RULE FOR 8If a number is divisible by eight the last three digits are divisible by 8
Example : 4857248 
3. AWESOME DIVISION RULE FOR 11If a number is divisible by eleven the difference between the sum of the digits in the even places and the sum of the digits in the odd places is 11 or 0. 2 + 4 + 5 = 11 and 60852 is shown to be divisible by 11 because

4. Amazing number 4With number 4 the secret steps in the multiplication tables become a little more intricate.
At first the sums of the digits look like a jumble of figure, but choose at random any sequence of numbers and multiply them by 4 and you will see the pattern emerge of two interlinked columns of digits in descending order. 2160*4 = 8640 — 8+6+4+0 = 18 ———– 1+8 = — 9 
5. The 11 RuleYou likely all know the 10 rule (to multiply by 10, just add a 0 behind the number) but do you know the 11 rule? It is as easy! You should be able to do this one in you head for any two digit number. Practice it on paper first! To multiply any two digit number by 11:
The only thing tricky to remember is that if the result of the addition is greater than 9, you only put the “ones” digit in the hole and carry the “tens” digit from the addition. For example 11 x 57 … 5__7 … 5+7=12 … put the 2 in the hole and add the 1 from the 12 to the 5 in to get 6 for a result of 627 … 11 x 57 = 627 
6. Percentage computationCalculate 65% of 460:
Example :
Calculate 67.5% of 460: 
7. To calculate reminder on dividing the number by 7 11 and 13Let me explain this rule by taking examples consider the number 4523895099854 
8. Square a 2 Digit Number Ending in 5For 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 (2×3) · Take the result (2×3=6) and put 25 behind it. Result the answer 625. Try a few more 75 squared … = 7×8=56 … put 25 behind it is 5625.

9. Square 2 Digit Number: UPDOWN MethodSquare a 2 Digit Number, for this example 37: · Look for the nearest 10 boundary · In this case up 3 from 37 to 40. · Since you went UP 3 to 40 go DOWN 3 from 37 to 34. · Now mentally multiply 34×40 · The way I do it is 34×10=340; · Double it mentally to 680 · Double it again mentally to 1360 · This 1360 is the FIRST interim answer. · 37 is “3” away from the 10 boundary 40. · Square this “3” distance from 10 boundary. · 3×3=9 which is the SECOND interim answer. · Add the two interim answers to get the final answer. · Answer: 1360 + 9 = 1369 
10. Finger Math: 9X RuleTo multiply by 9,try this: This works for anything up to 9×10! 