Math Tricks
Fast Math Made Easy
R. J. Clarke
Copyright 2018 R. J. Clarke
All rights reserved.
Contents
Finger Math Tricks
Finger Skip Counting
Using your fingers to skip count is an effective way to do the times tables. Start by holding both of your hands out. Then skip count in the first multiple on your fingers. Then you stop skip counting once you reach the finger that equals the second multiple
For example, if we wanted to find the answer to 5 x 7 we would keep adding 5 on each finger and stop on the seventh finger to give the answer 35
Finger 9 Times Table
The 9 times table from 1 to 10 can be done on your hands. Simply hold both of your hands in front of you. Then imagine that each finger is numbered from 1 to 10 with the left thumb representing 1 and the right thumb representing 10. If 9 is multiplied by a number, bend the finger that represents it. In the example below, 9 is multiplied by 4 so the fourth finger is bent
To get the answer to 9 x 4, we count the fingers to the left of the bent finger. There are 3 fingers and the answer is in the tens unit so this represents 30. Next, we count the fingers on the right of the bent finger. There are 6 fingers and the answer is in the single units so this represents 6. Put the two together and the answer is 36
Finger 6, 7, 8 , 9 And 10 Times Table
The numbers 6, 7, 8, 9 and 10 can be multiplied with each other using your hands. Begin by holding your hands in front of you so that you can see your palms. Then imagine that the fingers on each hand is numbered from 6 to 10 with 6 on the thumbs and 10 on the little fingers. If a number between 6 and 10 is multiplied by another number between 6 and 10, touch the fingers together to represent them. In the example below, 8 is multiplied by 7 so those fingers are touching
To get the answer to 8 x 7, we count the fingers that are touching as well as those above. There are 5 fingers and the answer is in the tens units so this represents 50. Next, we count the fingers below the touching fingers. There are 2 on the left and 3 on the right. These need to be multiplied together so 2 x 3 = 6. The answer is in the single units so this represents 6. Put the two together and the answer is 56
Finger Trigonometry
To do basic trigonometry on your fingers, start by holding out your left hand and imagine that each finger is numbered in degrees. The thumb represents 90 o whilst the little finger represents 0 o . Then bend the finger that corresponds to the degrees that you want to find out
To find the Sin, do the square root of the number of fingers below the bent finger. Then divide by 2
Sin30 o =
To find the Cos, do the square root of the number of fingers above the bent finger. Then divide by 2
Cos30 o =
Tan equals Sin divided by Cos. Therefore to find the Tan, do the square root of the number of fingers below the bent finger. Then divide by the square root of the number of fingers above the bent finger
Tan30 o =
Multiplication Tricks
Friendlier 5 Times Table
Halve the number that is being multiplied by 5.
Then add a zero on the end
For example:
26 x 5 = ?
= 13
Then add a zero on the end to give:
If there is an odd number being multiplied by 5, then you look at the number below to make it an even number. Halve it and then add a five on the end
For example:
23 x 5 = ?
= 11
Then add a five on the end to give:
Simpler 6 Times Table
Any even number multiplied by 6 causes the last digit of the answer to be the same
For example:
6 x = 1
6 x = 2
6 x = 3
Now that we know how to find the last digit of the answer, it is time to learn how to find the first digit of the answer. Start by halving the second number so that would be 16 divided by 2 in the example below
Then add the first digit of the second number. In this example, the first digit of 16 is 1 so this number needs to be added to 8
16 / 2 = 8
8 + 1 =
The first digit of the answer is 9. We then put the first and second digits together to give the final answer:
6 x 16 =
Easy 11 Times Table
The easy way to do the 11 times table for small numbers from 1 to 9 is to duplicate the first digit. For example:
3 x 11 = 33
4 x 11 = 44
5 x 11 = 55
With large numbers such as: 34 x 11 = ?
Split the first number in half. For example:
3 _ 4
Then add both of the numbers together (3 + 4 = 7) and then this number goes into the middle
Therefore the answer is 3
With large numbers such as: 57 x 11 = ?
Split the first number in half. For example:
5 _ 7
5 + 7 = 12
The second digit of 12 stays in the middle.
The first digit is carried over and is added to the 5
Therefore the answer is 6
12 Times Tables And Beyond
To multiply a number by 12, the first digit of the answer is the same as the number it is being multiplied by. The other digits of the answer can be found by multiplying by 2 (the second digit of 12) and then adding the next digit to it from the right. For example:
321 x 12 = ?
st DIGIT: 3 =
nd DIGIT: 3 x 2 + 2 =
rd DIGIT: 2 x 2 + 1 =
th DIGIT: 1 x 2 + 0 =
321 x 12 = 3852
To multiply by 13, use the same method but multiply by 3 (the second digit of 13) instead. For example:
321 x 13 = ?
st DIGIT: 3 =
nd DIGIT: 3 x 3 + 2 =
rd DIGIT: 2 x 3 + 1 =
th DIGIT: 1 x 3 + 0 =
Since the 2 nd DIGIT answer is a double digit number, carry the first digit of the 11 over to the 1 st DIGIT answer. This gives 3 + 1 =
321 x 13 = 4173
Line Multiplication
If we have the math problem of 21 x 13 = ?
Start by drawing parallel lines to represent 21. Then draw the lines in the different direction to represent 13
Next, draw a circle to separate the points of interception and count them up, starting from the right
This method can also be used on harder math problems such as: 211 x 24 = ?
