Multiplying Whole Numbers Close to Each Other

These multiplication tricks will only work for you if you have memorized or can quickly calculate the square of numbers. Learn the trick of finding square of any two digit number.  Also master the shortcut to find the square of any number.

Multiplication of Two Numbers that Differ by 2

When two numbers differ by 2, their product is always the square of the number in between these numbers minus 1.

1. 18*20 = 19^2 – 1 = 361 – 1 = 360
2. 25*27 = 26^2 – 1 = 676 – 1 = 675
3. 49*51 = 50^2 – 1 = 2500 – 1 = 2499

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Quick Multiplication by 5

Tricks for fast calculation by 5

It is a simple trick which is very intuitive and easy to understand. Many followers might find it very simple. However, there are many who will enjoy this simple yet readily usable trick to multiply any number by five.

1. Multiplying 5 times an even number: halve the number you are multiplying by and place a zero after the number.


i. 5 * 136, half of 136 is 68, add a zero for an answer of 680.

ii. 5 * 874, half of 874 is 437; add a zero for an answer of 4370. Read More

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How to Find Square of Numbers Ending in 9

Squaring any number ending in 9

We can easily calculate the square of any number ending in 9 using the method described in this post. Let us understand this method with the help of an example –

Finding the square of 39

Firstly add 1 to the number. The number now ends in zero and is easy to square.
40^2 = (4*4*10*10) = 1600. This is our subtotal.

In the next step, add 40 plus 39 (the number we squared plus the number we want to square) Read More

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Ratio of Area and Volume

Finding the ratio of areas or volumes given the length of a side of a 2 or 3 dimensional figure was always a time consuming task. With the help of the knowledge you are going to acquire now, this will be a simple and quick task.

In any two dimensional figure, if the corresponding sides are in the ratio a:b, then their areas are in the ratio a2:b2

Two dimensional figures can be any polygon like square, rectangle, rhombus, trapezium, hexagon, etc. It can also be a triangle or a circle. The sides, referred in the statement above, can be length, breadth or even diagonal in case of a polygon. In case of a circle the sides will be represented by radius or diameter or circumference. In triangle it can be sides or height of a triangle. Read More

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No More Carrying Over

“Carry” in Addition – Can it be Avoided?

Carrying over is a concept taught to us at a very early stage of our life. However, it has never been an easy thing to do. In adding two or more numbers, most of us face problem while “carrying over”. Larger the digits, involved in the numbers to be added, more likely it is to involve carrying.   More the carrying over involved, more likely are we to make mistakes.

Friends, remember the most basic and effective rule of making arithmetic fast and quick is to break difficult calculations into simpler, easily manageable small calculations.

Any digit when added to 9 (except 0) makes carrying over mandatory.  On the contrary, anything added to 0 can’t produce a two digit number.  Even if 9 is added to 0, no carrying is needed. Read More

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Rule of 72 – Estimation of Compound Interest and Time

Effect of Compounding

The Rule of 72 is a good quick math shortcut to find out the following –

  • Time required for an amount to double itself, at a given rate of interest
  • Rate at which an amount should grow to double itself in given time

This formula can be applied for “Doubling Problems” related to money, population, etc. which grows at an annual compounded rate.


  1. To calculate the time; T = 72/R
  2. To calculate the rate of interest; R= 72/T Read More
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Trick for Adding Time

Have you ever faced any problem in adding time?

If you have ever have faced the slightest difficulty in adding time or duration expressed in hours and minutes, this trick is meant for you.

Say you have to add 4 hours 55 minutes and 2 hours 40 minutes.

Make 4 hours 55 minutes into one number, which will give us 455 and do the same for the other number, 2 hours 40 minutes, giving us 240.

Shortcut Trick to Add Two Numbers Read More

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Simplify Multiplication with the Lattice Method

Simplify Multiplication using Lattice Method

Multiplication tables are a pillar of growing up no matter where you are in the world. Spending most of fourth grade learning how to multiply up to 12 x 12 was a fun and exciting time, but I was never a fan of how long it took to multiply larger numbers. I didn’t learned the lattice method until later but as a fan of matrices in calculus, this alternative method of multiplication appealed to me. Here’s how it works:


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Quickly Multiply by 21

Rule for multiplying any number by 21

Start from left. Double the first digit and add it to left side neighboring digit. Repeat the steps for subsequent digits. The last number will be same as the last number of the multiplied number.


This rule is very much like the shortcut for multiplying by 11. Since 21 is sum of 11 and 10, it does belong to the same family of short cuts.

Let’s understand the whole concept with an example. Let’s multiply 5392 by 21.

The first digit of the answer will be equal to twice the first digit of 5392. To make the rule consistent assume there is a zero before the number. Read More

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Shortcut for Addition of Consecutive Numbers

In this post I’ll share with you a useful shortcut maths trick for “finding out the sum of consecutive numbers”. For example, this trick I am talking about can help you in finding the sum of all the numbers from 23 to 31 or any other set of numbers.

Shortcut Addition Trick

Add the smallest number to the largest number of the given set of consecutive numbers. Then multiply the result by the number of numbers in the set. Finally divide the result by two.

Solving the above example, let’s find: 23+24+25+26+27+28+29+30+31 Read More

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