MATH MAGIC
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Transcript of MATH MAGIC
20 August 2013
MATH MAGIC
20 August 2013
MULTIPLICATION TRICKS
CROSS-MULPLICATION
14 X 12
First, to get the last digit in the answer, multiply the two numbers on the right. Write the answer, as the rightmost digit in the problem’s answer.
2x4=8
14 X 12
8
Now, get the middle digit, cross-multiply both sets of numbers, and then add the together.
1 x 2 = 21 x 4 = 4
6
14 X 12
68
Lastly to get the last digit, simply multiply the left digits.
1 x 1= 1 14 X 12
168
TRY!
28 X 23In this case, we will do the carrying
procedure.
COMPLEMENTARY MULTIPLICATION
96 x 94
First, subtract both numbers in 100 and list the difference.
100 - 96 = 4 100 - 94 = 6
Second step is to subtract diagonally. You will notice there that they will give the same answer, and this will be your base number.
96 – 6 = 9094 – 4 = 90
96 x 94
90
Third, multiply the two numbers we got by figuring the difference between the original numbers and 100.
4 x 6 = 24
•Lastly, write it to the right of the base number.
96 x 94
9,024
•If the number are larger than 100, add the difference instead of subtracting.
Ex. 103
x 107
103 – 100 = 3 107 – 100 = 7
103 + 7 = 110107 + 3 = 110
•You will arrive with same answer then write it as the base number.
103 x 107
110
•Multiply the 3 and 7, then write it as the base number.
3 x 7 = 21
103 x 107
11,021
This method is applicable also in numbers around 50.
Ex.
46 x 44
MULTIPLYING BY 11
18X 11
•Add the two digits and insert the sum between the digits.
1 + 8 = 9
18 X 11
198
99 X 11
In case that you got a two-digit number, add that numbers’ left digit to the digit in the original number.
9 + 9 = 18
99 X 11
1,089
SQUARING TRICKS
Squaring a number around 100
If the number falls under 100 and above 50, you simply figure the difference between 100 and the number.
96²
•Subtract the difference from the number being squared, and write the answer as the first digits in your answer.
100 – 96 = 4
96² - 4
92 base number 92(00)
•Take the difference between 100 and the number being squared and square.
100 – 96 = 44² = 16
•Place that number after the base number and you have the answer.
96² = 9,216
If the number to be squared is more than 100, add the difference to the number.
Squaring numbers that ends in 5
Any number that ends in 5 is easy to square to start with, you know that
5 x 5 = 25, so the answer will automatically end in 25.
Ex. 35²
•Add 1 to the first digit, ignore the rest at the number.
1 + 3(5)
4
•Multiply the result to the first digit of the original number. This result is the first part of the answer.
4 x 3 = 12
12 with 25 makes 1, 225.
Try! 85² 115²
65²
SHORTCUT AND HELPFUL HINTS
18 X 101 = 1,81884 X 101 = 8,48497 X 101 = 9,797
102 X 101 = 10,302621 X 101 = 62,721
Thank you!