7 Mathematics Shortcuts That Can Blow You Down

Addition

If you want to summon a mind calculator for adding three-digit numbers, here's the trick -

To find the result to this problem, 263 + 726, round up both the numbers and add.

That makes it 270 + 730 = 1000.

Now subtract the difference from the rounded numbers.

270 - 263 = 7, 730 - 726 = 4

Add the balance, 7+4=11.

Subtract this balance from the sum of the rounded numbers.

That makes it 1000 - 11 = 989.

Subtraction

Did you know how quick it is to subtract a number from 1000? "What is 1000 - 737?" someone might ask. Don't blink, try this hack.

Minus the first two digits from 9 and the last digit from 10.

9 - 7 = 2
9 - 3 = 6
10 - 7 = 3

The answer is 263.

Multiplication

Multiplying any number by 9 is a whale of fun, especially if it is a single-digit number. Just write the number 0 - 9 in ascending and descending order in parallel lines. That's the order of 9 tables! Can't believe it yet? Look for yourself!

0 9
1 8
2 7
3 6
4 5
5 4
6 3
7 2
8 1
9 0

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Division

It's not always multiples of 5 and 10 that are easily divisible numbers. Read on and learn more.

9 - Add all the digits of a number, eg., 466 - add 4 + 6 + 6. The sum is 18. Since 18 is divisible by 9, 466 is divisible by 9, too.
8 - In case the last three digits are evenly divisible by 8 or are 000.
6 - First check if it is an even number, also, the digits when added together should give you a number divisible by 3.
5 - In case the number ends in a 0 or 5.
4 - In case the number ends in 00 or a two-digit number that is evenly divisible by 4.
3 - In case the digits are added together and the output is evenly divisible by 3.
2 - If it ends in 0 or an even digit - 2, 4, 6 or 8.

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Quick Percentage

What is 30% of 50?

Multiply the numbers 30 x 50 = 1500.

Remove the last two zeros. The answer is 15%.

In case you are wondering what to do when they are not round numbers, round the numbers and multiply to get a rough estimate first. You can work on the accuracy after that.

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Approximate Square Roots

It is simple to answer the square root of single digits like 9 or 8 . But what
do you do when asked the square root of 98?

Don't panic. Follow this simple method. You know square of 9 is 81 and the square of 10 is 100. So the answer for square root of 98 must be 9 point something!

11 Magic

Multiplication with 10 is not the only easy times table. Any number multiplied with 11 is equally easy to calculate. Want proof?

Take 43 x 11.

Leave a space between the existing numbers. Say 4_3. Now add up the numbers 4 (4 + 3) 3. The answer is 473. Just in case, the sum makes a two digit, you can carry it over.

Ex: 47 x 11 = 4 (4 + 7) 7.

(4 + 1) 17 = 517.