Question
Fill the box using 1, 3, 5, 7, 9, 11, 13, 15. You can repeat the numbers.
Keys
We can't obtain an even number 30 by just choosing three numbers, because the result is always odd. Let's think outside the box.
'Reversing' method.
Decimal numbers.
Borrowing numbers from other number systems.
Solution
Sol. 1
It is a commonly seen method in various riddle videos. So, here it is.
Reverse upside down to get .
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Sol. 2
Let us repeat the number below the decimal point.
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Sol. 3
The number represents '11 in base 9.' It is just 10.
We have base 9.
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Or, we could use base 7. is the number 10.
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More information
In base 9, each digit value is a power of .
Similarly, in base 7, each digit value is a power of .