Free Math Tips: January 2010

Mathematical trick: multiply by powers of 2

Wednesday, January 13, 2010

Students who follow courses in electronics and systems know that it is essential to know the binary system and as a result quickly calculate the powers of 2 of a number. As repeatedly explained below, the lecture method, with a little 'training will make you fast in mental calculation. To multiply a number by 2, 4, 8, 16, 32 or any other power of 2 is sufficient to double the product as many times...

Mathematical trick: multiply a number by 5, 25 or 125

Multiply by 5 Multiplying a number by 5 and multiply it by like 10 and then divide by 2. Remember that (obvious but better remembered) that multiplying a number by 10 means add one zero to the bottom of the number. 16 × 5 = (16 × 10) / 2 = 160 / 2 = 80 Another example: 82 × 5 = (82 × 10) / 2 = 820 / 2 = 410 Again 6840 × 5 = 68400 / 2 = 34200 Multiply by 25 Multiplying a number by 25 you multiply...

Mathematical trick: multiply by 11

To multiply a number by 11 and add enough pairs of numbers from right within the given number except the numbers on the edges that should be repeated. For example: consider the following product: 324 x 11 * From the right type 4 (the last number to the right of 324) first digit of the product; * Try the sum 4 +2 = 6 (the sum of 1 'and 2' figure), you get the second digit of the product; *...

Mathematical trick: multiply a number by 9, 99 or 999

Very often I hear from students' math is one thing to genes and the affirmation that I hate more: "I am not inclined towards mathematics, but only for matters literary" I'm thinking that if a student says this is because believe someone has done this. In my opinion we are all potentially good at mathematics and literature. Use the brain may be faster than using a calculator just to do some 'training...

Dividing by 14

Tuesday, January 12, 2010

Sara Heikali builds on her divisibility test for seven: How can you know if a number with three or more digits is divisible by the number fourteen? Check if the last digit of the original number is odd or even. If the number is odd, then the number is not divisible by fourteen. If the number is even, then apply the divisibility rule for seven. (Keep in mind, the odd and even test is to see...

Dividing by 13

Here's a straightforward method supplied by Scott Fellows: Delete the last digit from the given number. Then subtract nine times the deleted digit from the remaining number. If what is left is divisible by 13, then so is the original number. Rafael Ando contributes: Instead of deleting the last digit and subtracting it ninefold from the remaining number (which works), you could also add the deleted...

Dividing by 11-2

Any number written in our decimal system is made up of powers of 10. For example, 65,321 = 6(10^4) + 5(10^3)+3(10^2) + 2(10)+1. Now if you are interested in knowing whether 65,321 is a multiple of 5 (that is, is exactly divisible by 5), you can tell just by looking at the last digit. That's because 10^4, 10^3, 10^2, and 10 are all divisible by 5, so the last digit on the end gets to cast...

Dividing by 11

Let's look at 352, which is divisible by 11; the answer is 32. 3+2 is 5; another way to say this is that 35 -2 is 33. Now look at 3531, which is also divisible by 11. It is not a coincidence that 353-1 is 352 and 11 × 321 is 3531. Here is a generalization of this system. Let's look at the number 94186565. First we want to find whether it is divisible by 11, but on the way we are going to...

Dividing by 8

Check the last three digits. Since 1000 is divisible by 8, if the last three digits of a number are divisible by 8, then so is the whole number. Example: 33333888 is divisible by 8; 33333886 isn't. How can you tell whether the last three digits are divisible by 8? Phillip McReynolds answers: If the first digit is even, the number is divisible by 8 if the last two digits are. If the first digit...

Dividing by 7

To find out if a number is divisible by seven, take the last digit, double it, and subtract it from the rest of the number. Example: If you had 203, you would double the last digit to get six, and subtract that from 20 to get 14. If you get an answer divisible by 7 (including zero), then the original number is divisible by seven. If you don't know the new number's divisibility, you can apply the...

Math Games & Lessons : Math Tricks With Numbers

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A way to remember the Entire Unit Circle for Trigonometry

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Fun Math Trick! Squaring Numbers Near 100

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Quick Math Tricks: Thinking of Numbers as Blocks

Quick Math Tricks: Thinking of Numbers as Blocks -- powered by eHow....

Understanding Math : Math Tips & Tricks

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Math Tips and Tricks- Multiply by 11 and 111

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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...

The 11 Rule

You 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: For this example we will use 54. Separate the two digits in you mind (5__4). Notice...

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...

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...

Square 2 Digit Number: UP-DOWN Method

Square 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 34x40 The way I do it is 34x10=340; Double it mentally to 680 Double it again mentally to 1360 This 1360 is the FIRST interim answer. 37...

Multiply By 4

To quickly multiply by four, double the number and then double it again. Often this can be done in your head. ...

Multiply By 5

To quickly multiply by 5, divide the number in two and then multiply it by 10. Often this can be done quickly in your head. ...

The 11 Rule Expanded

You can directly write down the answer to any number multiplied by 11. Take for example the number 51236 X 11. First, write down the number with a zero in front of it. 051236 The zero is necessary so that the rules are simpler. Draw a line under the number. Bear with me on this one. It is simple if you work through it slowly. To do this,...

Wednesday, January 13, 2010

Tuesday, January 12, 2010

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