## Hello Friends ! Welcome Today we are going to discuss some of the puzzles, challenges or brain teaser which are viral in social media such as Face book ,whats app, twitter and Google+ etc. which are based on Mathematics directly or indirectly . You have seen such types of puzzles mentioned 99.9% Fail , Solve if you are genius like this........ Let us try to discuss and solve them.  PUZZLE # 1 Which number should replace the ?

4 ,  9 ,  19  ,  39  , 79   ?

## Even Number

When any Number is divisible by  2 then that number is called An Even number . If we take 2,16,84,22,20,100 etc then they are Even Numbers as they can be divided by 2.

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## Odd Number

When any number is NOT divisible by  2 then that number is called An ODD number .If we take 21,15,49,21,57,101 etc then they are Odd  Numbers as they can NOT  be divided by 2.

## A Multiple of 3

An number which is divisible by 3 or which comes in the  table of 3 is called  multiple of 3. if we take 57,102,69,9,6,21,39 etc numbers , as these numbers comes in the table of 3 or these are divisible by 3 , so they are Multiple of 3.

## Prime Number

Any number which has only two Factors 1 and the numbers itself is called Prime number. 1 is not the the prime number, 2 ( It is the 1st prime number ) , 3,5,7,11,13,17,19,23  etc  are examples of Prime numbers as these numbers have only two factors 1 and the number itself.

## Square Number

Any number whose square root is a Natural  number is called square Number . such as  1,4,9,16,25,36,49,64,81,100,121,144 etc.

## Factors of 360

All those numbers which can divide 360 are called factors of 360 .Here We can take such numbers as 1,2,3,4,5,6,8,9,10,12,18,36 etc

## So Final Answer will be 200

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There are two numbers 'a' and 'b' in 1st and 2nd columns then 3rd column has been  occupied by their combination as follows

a*b = (a2  + b2 ) - 1,
1*3 = (12  + 32 ) - 1 = ( 1 +   9) -1  = 10 - 1 =  9
3*4 = (32  + 42 ) - 1 = ( 9 + 16) -1  = 25 - 1 = 24
2*5 = (22  + 52 ) - 1 = ( 4 + 25) -1  = 29 - 1 = 28
4*5 = (42  + 52 ) - 1 = (16 + 25) -1 = 41 - 1 = 40

So 40 will replace  ?  in this puzzle
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