Learning to perform fast mental maths** **calculation will help you immensely irrespective of which field of life you deal with.Knowing these mental maths tricks will give you a positive edge over the others.Whether you are a student,aspiring engineer,statistician,scientist,school teacher or anyone else dealing with numbers,learning this quick mental tricks and techniques

**Multiplication of any two digit number by 11**

**Divisibility of any number by 3 or 9**

**Example**

**3) Multiply any large number by 12 mentally in seconds**

**Step 1:**021314 * 12 = _____8 (Double of Last Digit 4= 8 )

**Step 2:**021314 * 12 = ____68 (Now Double 1= 2, and add it to 4, 2+4=6)

**Step 3:**021314 * 12= ___768 (Now Double 3=6, and add it to 1, 6+1=7)

**Step 4:**021314 * 12= __5768 (Now Double 1=2, and add it to 3, 2+3=5)

**Step 5:**021314 * 12= _55768 (Now Double 2=4, and add it to 1, 4+1=5)

**Step 6:**021314 * 12= 255768 (Now Double 0=0, and add it to 2, 0+2=2)

**21314 * 12 = 255768**

**Calculating Square of numbers quickly…**

Multiply the last digits of both the numbers ; thus ___ 5 × 5 = 25

now add 1 to 3 thus 3 + 1 = 4

multiply 4 × 3 = 12

thus answer 1225

Let the number 49 . Look for the nearest multiple of 10 . ie; in this case 50. We will reach 50 if we add 1 to 49. So multiply (49+1) x (49-1) = 50 × 48 = 2400 This is the 1st interim answer.

We had added 1 to reach the nearest multiple of 10 that is 50 thus 1x 1 = 1 This is the second interim answer.

The final answer is 2400 + 1 = 2401 …

Another example

Let the number be 47 .

Look for the nearest multiple of 10 . ie; in this case 50. We will reach 50 if we add 3 to 47. So multiply (47+3) x (47-3) = 50 × 44 = 2200 This is the 1st interim answer.

We had added 3 to reach the nearest multiple of 10 that is 50 thus 3x 3 = 9 This is the second interim answer.

The final answer is 2200 + 9 = 2209 …

**Multiplication of 2 digit numbers from 11 to 10**

Take 2 numbers like 12 and 19

Place the larger number(19) at the top and the 2nd digit of the smaller number(2) in the bottom.

19

2

Add 19+2=21, Then multiply 21×10=210

Now, multiply the units digit of both numbers, i.e., 2×9=18.

Add the two numbers, 210+18 and the answer is 238

**Multiplication of any 3 digit numbers**

Now subtract the number at units place

108-8=100

106-6=100

Now select any number and add the unit digit of another number

108+6=114

Now multiply, 114×100=11400

Now multiply the unit digits of both numbers, 8×6=48

Add, 11400+48=11448

The product of the numbers 108 and 106 is 11148

**Few More example**

Now subtract the number at units place

202-2=200

206-6=200

Now select any number and add the unit digit of another number

202+6=208

Now multiply, 208X200=41600

Now multiply the unit digits of both numbers, 2×6=12

Add, 41600+12=41612

The product of the numbers 202 and 206 is 41612

**Some Important Multiplication which can be done quickly**

Multiply by 6: Sometimes multiplying by 3 and then 2 is easy.

Multiply by 9: Multiply by 10 and subtract the original number.

Multiply by 12: Multiply by 10 and add twice the original number.

Multiply by 13: Multiply by 3 and add 10 times original number.

Multiply by 14: Multiply by 7 and then multiply by 2

Multiply by 15: Multiply by 10 and add 5 times the original number, as above.

Multiply by 16: You can double four times, if you want to. Or you can multiply by 8 and then by 2.

Multiply by 17: Multiply by 7 and add 10 times original number.

Multiply by 18: Multiply by 20 and subtract twice the original number (which is obvious from the first step).

Multiply by 19: Multiply by 20 and subtract the original number.

Multiply by 24: Multiply by 8 and then multiply by 3.

Multiply by 27: Multiply by 30 and subtract 3 times the original number (which is obvious from the first step).

Multiply by 45: Multiply by 50 and subtract 5 times the original number (which is obvious from the first step).

Multiply by 90: Multiply by 9 (as above) and put a zero on the right.

Multiply by 98: Multiply by 100 and subtract twice the original number.

Multiply by 99: Multiply by 100 and subtract the original number

8)** How to quick convert kilos to pound**

Example

112 Kg

Step 1: Multiply by 2

112X2= 224

Step 2: Divide the previous one by 10

224/10=22.4

Step 3:

Add both the number

224+ 22.4= 246.4 pounds

9) **How to quickly add time**

Example

1 hr 35 min and 2 hr 46 min

Step 1 . Treat them as number

135 and 246 .

Now add them = 381

Step 2 . Add 40

381+ 40 = 421

So total time is 4 hours and 21 min

10) **How to quickly perform temperature conversion from Fahrenheit to Celsius or Celsius to Fahrenheit**

Example

- 100 F

Subtract 30 and divide by 2

100-30 =70/2=35 C

2) 30 C

Double it and 30

30X2=60+30= 90 F

So clearly Knowing these simple calculation techniques gives you an advantage over others and can get you a job,get you crack any competitive exams and much more.

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