Simple math tips & tricks for multiplication and divisibility check.

1. Welcome to the World of
MATHEMA-TRICKS
Minhas Kamal

2. Today we will learn some cool
math tricks.
So that, we can use more our
brain and less our calculator.
1

3. Square a two digit number
ending in 5
For example: 152, 452, 852
2

4. Square a two digit number ending in 5
Lets consider the number 35.
1. We take the first digit and multiply it with it’s next
number.
3 5
3 * 4 = 12
2. Then simply put 25 after it.
1 2 2 5
So, 352 = 1225
3

5. Square a two digit number ending in 5
Here is another example:
Step-1:
9 5
9 * 10 = 90
Setp-2:
9 0 2 5
So, 952 = 9025
4

6. Multiply any number by 4
Simply double the number two times.
5

7. Multiply any number by 4
Take the number 63
63*4 = 63*(2*2) = (63*2)*2 = 126*2 = 252
Lets try another number 753
double of 753 = 1506
double of 1506 = 3012
So, 753 * 4 = 3012
6

8. Multiply any number by 5
Simply half the number &
multiply it by 10.
7

9. Multiply any number by 5
Take the number 86
86*5 = 86*(10/2) = (86/2)*10 = 43*10 = 430
Lets try another number 495
half of 495 = 247.5
247.5 * 10 = 2475
So, 495 * 4 = 2475
8

10. Multiply any number by 15
Multiplication by 10 +
Multiplication by 5.
9

11. Multiply any number by 15
Take the number 84
84*10 = 840
84*5 = (84/2)*10 = 42*10 = 420
84*15 = 840 + 420 = 1260
Lets try another number 495
495*15 = 495*10 + 495*5
= 4950 + (495/2) * 10
= 4950 + 2475
= 7425
10

12. Multiply any number by 11
x y z
x y + z zx + yxyz * 11 =
11

13. Multiply any number by 11
Take the number 263
Lets try another number 485
2 6 3
2 9 38263 * 11 =
4 8 5
5 3 53263 * 11 = 11
12

14. Multiply two numbers
between 10 and 20
For example: 15*17, 19*13
13

15. Multiply two numbers between 10 and 20
Lets consider the number 12*14.
1. Add the first number with the other number’s
second digit.
1 2
+ 1 4
1 6
2. Place a 0(zero) after it.
1 6 1 6 0
14

16. Multiply two numbers between 10 and 20
3. Multiply the second digits of the two numbers.
1 4
* 1 2
8
4. Add this number with the step-2 result.
1 6 0
+ 8
1 6 8
So, 12*14 = 168
15

17. Multiply two numbers between 10 and 20
Here is another example: 17*13
Step-1: 17 + 3 = 20
Setp-2: 20 200
Step-3: 7 * 3 = 21
Step-4: 200 + 21 = 221
So, 17*13 = 221
16

18. Divisibility Check
For example: is 7403 is divisible
by 11 ?
17

19. Divisibility Check (for 2, 3)
A number is divisible by 2 if its last digit is 0, 2, 4,
6 or 8. For example: 12, 5394, 993120.
A number is divisible by 3 if sum of its digits is
divisible by 3. For example: 72 is divisible by 3 as
7+2=9 which is divisible by 3.
Another example: 57381, 5+7+3+8+1=24; 24 is
divisible by 3. So 57381 is also divisible by 3.
18

20. Divisibility Check (for 5, 7)
A number is divisible by 5 if its last digit is 0 or 5.
For example: 100, 3795, 698170.
For 7, separate & double the last digit of the
number. Then subtract it from the rest. Take: 91.
91 9 1 9 - (1*2) 7
Now, if the number is 0 or divisible by 7, then
the original number is also divisible by 7.
19

21. Divisibility Check (for 7)
If the number is big then continue the process as
many time as needed.
Lets take 3752.
3752 375 – 2*2 371 37 – 1*2 35
Now, 35 is divisible by 7. So, 3752 is also divisible by 7.
Youmayhavegoneevenfurther,
35 3-5*2 -7 ; whichisalsodivisibleby7.
20

22. Divisibility Check (for 11)
For 11, add and subtract digits in an alternative
pattern (like- 1st digit - 2nd digit + 3rd digit …).
Take:8525
8-5+2-5=0
So,itisdivisibleby11.
Take:392755
3-9+2-7+5-5=-11
Alsodivisibleby11
21

23. Divisibility Check (for 13)
For 13, add 4 times of the last digit to the rest of
the number. Take: 351
351 35+1*4 39
Itisdivisibleby13.
Letstryanother:754
754 75+4*4 75+16 91 9+1*4 13
So, you know.
22

24. So we have leant a lot of math
tricks today.
Practice to make them perfect
for you.
23

25. There is one math trick only for
YOU!
24

26. Lets see if you can do it right!
25

27. Add these numbers one after another-
1000
20
26

28. Add these numbers one after another-
1000
20
1000
30
26

29. Add these numbers one after another-
1000
20
1000
30
1000
40
26

30. Add these numbers one after another-
1000
20
1000
30
1000
40
1000
10
26

31. Add these numbers one after another-
1000
20
1000
30
1000
40
1000
10
5000 ???
26

32. Add these numbers one after another-
1000
20
1000
30
1000
40
1000
10
5000 ???
If your answer is 5000,
then you are among the
most who mistook. The
actual answer is 4100.
Count again and see if
you get it right this time.
26

33. www.facebook.com/think.stupid.eduwww.youtube.com/c/thinkstupidedu