PLACE THE NUMBERS

Enter all of the following numbers in the circles:

2, 3, 4, 5, 6, 7, 8, 9, 10

Numbers 2 and 5 are already inserted.

The insertion must be done in such a way that by adding three aligned numbers, you always get as sum 21.

Question: if you want to know the value to insert in correspondence of the circle with the “?” how many numbers must be entered at the minimum?

SOLUTION

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SOLUTION: The unknown number is 4.

SOLUTION: it is sufficient to enter 3 other numbers (in addition to 2 and 5) to calculate the number 4. In particular, the exercise is solved quickly by immediately identifying the position of the number 9.

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