You see a heavy stone door sealed shut. Beside it stands a contraption:
A stone pedestal with five shallow depressions, each the size of a fist.
Nearby are five iron spheres, each of identical size but marked with different weights etched in runes:
1, 2, 3, 4, and 5.

Above the door, an inscription reads:

"To pass through stone, balance the scale.
The outer weights must equal the center."

You realize:

• The five depressions are in a line: [ _ _ _ _ _ ]

• You must place one sphere in each slot.

• When the correct combination is set, the door will open.

Solution Logic:
The sum of the two outer weights (positions 1 and 5) must equal the middle weight (position 3).