An easy puzzle

Number Theory Level 1

Can you find the number ?? You can find the missing number by the strength of observation or by building a base calculation also depends on the strength of observation ..


The answer is 91.

Ahmed Salah by Ahmed Salah , 24, Egypt

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3 solutions

Hans-Derek Yu
Jun 18, 2014

The sum of the white numbers in each row is double the colored number in each row.. Thus, 91 fills the box.

1 Helpful 0 Interesting 0 Brilliant 0 Confused

I don't know why it works, but I had: 'second number' * 'row number' + 'colored number' = 'second to last number'

3 * 1 + 12 = 15,

4 * 2 + 20 = 28,

5 * 3 + 30 = 45,

6 * 4 + 42 = 66,

7 * 5 + 56 = 91

1 Helpful 0 Interesting 0 Brilliant 0 Confused

The last number of each row is the product of the 2nd and 3rd number of the same row...

The second last number of each row is the last number plus the second number times the row number...For example, in the first row...the last number is 12, the second last number is : 15 (second last no.) = 12 + (3 (2nd no.) x 1 (row number)) .So the second last number of the fifth row = 56 + (7 (2nd no.) x 5 (row no.)) = 91

1 Helpful 0 Interesting 0 Brilliant 0 Confused

What about: the second last number of each row is the sum of the first 2 numbers multiplied by the second number.

So the second last number of the fifth row = (6 + 7) x 7 which = 91

Guiseppi Butel - 7 years ago

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good observation !!!

Ahmed Salah - 7 years ago

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