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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